You might want to look for a Chromecast Audio (CCA) on eBay – much better built-in DAC, cheaper than a Pi.
Or you could do what I have in my kitchen, a Google Home Mini on a plug adapter so that it just plugs into a socket. Great as a kitchen timer as well as a Roon endpoint.
One further thought. It might be worth considering a Qobuz subscription.
It could save ripping your collection as well as the cost of an additional hard drive and offer better quality recordings.
The issue may be whether it has everything you want. Against that it will also have far more to enjoy. You could always begin with a free trial.
Tidal is also an option.
Hi. To clarify.
An endpoint is an audio output-you can use a ROCK NUC for that, but Roon don’t recommend it. Better they say to have separate endpoints (as you were describing using the Pis). I was saying that a good quality lengthy audio cable will likely cost more than a Pi 
NAS is fine for storage and playback, or at least it if for me! You can put a drive in your ROCK NUC if you want-you basically point Roon to your storage location and it will happily accept a NAS.
Does that make sense?
Thanks - that’s a great idea. We already have a Google Home Mini in the kitchen, so that’s a zero-cost, zero-effort solution. If we decide that the audio quality just doesn’t cut it (unlikely in a kitchen full of motorized appliances), we could try a higher fidelity Roon ready device at that point.
Thanks, but that’s a hard sell for us. We have rather eclectic tastes, and many of our CDs had limited production runs and disappeared from circulation long ago - even more true for LPs. Also, I’m a semi-pro musician with a lot of recordings that have never been released commercially but that I’d like to have available, and they’re definitely not available publicly.
Still, an on-line streaming service has the virtue of introducing us to music we’d be unlikely to run across otherwise, so it’s still of interest just not a top priority.
Yes - I get it now! I had not come across the advice not to use one host device for both the Roon Core and for audio streaming. @Michael_Harris mentioned that a lot of people have success doing this, but it’s good to know that it’s not an optimal solution.
I’m learning about Raspberry HiPi and other Roon-Ready DACs, so something like that would probably be best for connecting to my main AV system.
Bruce, yes Roon do not recommend using the core as an end point, but many do, and have good results.
Personally I tried it once and with good USB suppression and an expensive cable there was no difference, but it was to test it and I never planned to continue using this.
I only mentioned it as someone else will, so always good to get both sides of that story.
I had bought two HifiBerry HATS for two Pi’s at the time and used those instead and they worked great until I moved on to Roon Ready streamers, but I still have them and they still work perfectly. You can build the whole of the streamer for not much more than £100 if you want to feed your amp over phono cables or SPDIF/Toslink. It’s often something I recommend to new starters as you learn a lot and the tinkering is on the easier side of the spectrum.
You can buy pure Roon Ready Streamers from about £400 that will feed your amp as above through SPDIF/Toshlink/Phono.
Thanks - that sounds perfect for me. It’s just the level of tinkering that I like, and I’m always happy to save a few $$ when I can.
I think what’s missing is a DAC on your Raspi. You can get a USB DAC or put a “Hat” on the Raspi and get audio out through a DAC with RCA R+L out or an Allo Digione provides Toslink to an external DAC.
I just used a Pi 3A with DietPi (over WiFi) and a USB out to a DAC and had occasional noise. The community here advised against WiFi and I switched to a Pi 4B and ethernet/Cat5 and haven’t had a problem since.
Another problem I had was the availability of any Pi now is terrible. (I have a two week old 3A for sale).
The above is for my high end speakers
For less critical listening - I also have Sonos speakers throughout the house.
Another option I considered (but couldn’t afford) is the Roon ready LS50 wireless.
Do you own the NUC ??? Or are you evaluating them? Intel (Windows) and Mac Minis are good choices.
I run my Roon core on a non-dedicated iMac and if I had a problem - I don’t know what it is…it sounds great.
Regarding you thoughts to use Raspberry Pi as endpoints. I do this VERY effectively. However, I caution you using ‘the analog out.’ The analog out from a RPi is based on the Pi’s DAC which is OK for computer sounds, but questionable for music play back. I use a ‘hat’ for converting the audio to coax digital in one case and a DAC hat for converting to analog audio. A hat increases the cost of the end point, but your ears will thank you over and over. Allo offers components or preconfigured solutions. Lead time is terrible right now.
excellent points. Also consider that the USB out of an rPi4B* is also good if feeding a DAC with a USB input.
*rPi3B+ and earlier have some sort of combined USB and ethernet connection, thus some don’t like the USB output on these units. I have no experience with this, as mostly have rPi4B units, and my one rPi3B+ has a hifiberry DIGI Plus “hat” that feeds S/PDIF into a DAC…
In my world, I want my music collection to be available wherever I am, so I keep all my music on a Synology NAS and use Audio Station/DS Audio for off premise listening. I run Roon on the NAS with no issues and use Roon for contemplative and exploratory in home listening. Roon on NAS ingests not just all of my music, but the .m3u playlists in AudioStation as well, many of which were created from Audio Station smart playlist functionality first. Audio Station can do some things that Roon cannot, including playlists generated from track years (Roon still only considers Album years, which doesn’t work for compilations).
As a result, I always have the same playlists on the road, and in Roon, and only have to manage them in AudioStation. I love that. A lot.
Welcome to Roon Bruce. You’re gettin a lot of advice here so I’ll abstain; you’re direction is good from what I can tell. Now, you just have to put all of it into the shaker with your own ideas and sort it out - not an easy task. Such is the blessing & curse of any such ‘community.’ 
Hi. Here’s my experience
NUC for the ROCK server has been bulletproof. NAS for files and Tidal for streaming.
For the kitchen I got 2 Google Nest Audio Speakers. You can set them up as a stereo pair. They use wifi and worked out of the box. Easy to use and the family is happy with them but not overly precise. NB you can use Roon to divide any 2 speakers into left and right, so the google functionality isn’t actually needed.
My garden office has some older Kef wifi speakers. They are a bit flakey as an endpoint so I have a Rasperry Pi with hat (fun project) feeding them. They sound fine.
Can use my phone as an endpoint / old school walkman while mowing the lawn.
Main listening area started off with the Receiver as an endpoint (surprised me that Roon found it). Then tried a Pi with Hat. Then realised the Receiver was doing A>D>A with an old internal DAC, so the Hat was useless anyway. Then long story and ended with a proper DAC feeding an analogue stereo. It’s actually using the NUC as an endpoint and I’ve had no problems. I’m not really sure what the problems are supposed to be.
Other tips
I used the core as an endpoint briefly before I found my 2x Squeezebox duets-never noticed any problems either. I was using it into an iLoud speaker, and then a pair of ancient (but surprisingly good) set of Bose computer monitor speakers. Living room set up is CXZ V2 into CXA81 via xlr.
Two points I didn’t see from others the first one I think you figured out yourself but here goes…
ROCK has no way to set-up “RAID”. But, yes, a stack of drives in this configuration is valid configuration if you run Roon Server on another operating system. As you mentioned though it may not provide any advantage. The music storage device does not need to be fast and it’s already recommended to backup away from the Core. One other thing I’ll mention on this topic is Roon does not expose the directory structure within the UX. For this reason you can point Roon at as many different drives as you want and all your music is presented the same. This makes it a lot easier to add more drives without having to shuffle things between them.
One advantage of using a NuC as an endpoint into a AV processor / receiver is you can use HDMI if you have any multichannel tracks. Something to think about once you upgrade the 990. In my main system I have a dedicated 2-channel endpoint and a HDMI endpoint for this exact reason. You can run ROCK on the NuC or just Bridge. When using ROCK as an endpoint no need to login or configure it. It will just show-up as an endpoint in Settings → Audio. I wouldn’t use a NuC as an endpoint with anything other than HDMI though. There are better / cheaper options to be had.
An anecdote
I have a 2TB hard disk in an old Synology NAS. It was their cheapest model, and slow at everything.
That is until I used it for music storage. I have a NUC/ROCK and the house router next to it on the main floor.
Music selection (several thousand tracks including hi-res) is basically a 1-2 second request. And I’m not setup ideally for playback … my basement endpoint is on WiFi and so is my laptop or phone as controllers. Doesn’t matter.
Roon library scans, when I drop a new album onto the watch folder, are pretty quick also.
I’ll change this to what was suggested above, using a simple external disk plugged into the NUC and have the NAS run regular backups. But even when doing it my way it’s still works well.
So yeah, you don’t need a RAID and I really don’t think you’d need an SSD either.
You’re pretty much on track. I’d suggest you look at the Allo Digital USBridge Signature with the Schiit Audio DAC of your choice. Schiit’s DACS have excellent sound and excellent USB interfaces. Even the $99 Modi is gorgeous. But it is a gateway drug by design. Let Modi in and your audio rack will become full of Schiit as excuses permit.
If you can, directly connect your Raspberry Pi endpoints. Ethernet is much more reliable than WiFi.
Amazon Eero WiFi is receiving good press. It is a mesh system that can be extended into remote corners by adding intermediate mesh nodes. It’s relaible and no fuss. Easy administration using the provided mobile app.
Roon’s recommendation to run Core on a NUC using ROCK is a good one for those of us who are not fiddly. Running Roon Core on mass market NAS is likely to disappoint as they don’t use ECC memory. The advantage to ROCK is that Roon Labs manages the Linux distribution for you. No need to watch for and periodically apply updates. ROCK will look after itself.
I recommend putting extra memory in your NUC as Linux will cache the active parts of the Roon database there.
Roon searches slow when Roon goes off to Qobuz for content. No way to improve that as Qobuz is outside the lifelines so to speak.
That said, I run Roon Core on a home brew NAS running TrueNAS Core (FreeBSD). The machine was spec’d with extra memory to run Roon Core in a virtual machine. I use POP_OS in the VM and run standard Linux Roon Core on top of POP_OS. It works great.
I highly recommend using a NAS for storage. Specifically TrueNAS from iX Systems. iX Systems TrueNAS Mini. Mine has run continuously for 5 years and I’m in the process of replacing aged disks. TrueNAS makes the replacement process easy. Off-line the tired disk. Shutdown (if needed) to replace the tired disk with a new one. Restart and add the replacement to the pool. Let TrueNAS sort itself.
TrueNAS Mini is designed to run continuously and does use ECC memory. ECC memory detects all 2 bit errors, recovers all 1 bit errors. Very important as Roon runs from memory once going. Poor experiences with Roon are almost always on non-ECC hardware.
I recommend using RAID-Z2 (double forward error correction). A second disk presented with symptoms while the first was reconstructing. Courtesy of RAID-Z2 we were still protected. Once the first disk was recovered, I repeated the process to replace the second.
If you use a NAS for music storage I recommend 2 things, ECC memory and hot-swap disk cases. I had a lot of fun with cables, a broken connector, etc along the way to replacing the first disk. If I were in a case like that iX Systems uses, I would not have had to muck around with cables. Much easier. Also, put disk serial numbers on the end frame so you don’t have to rack out a disk to check its serial number. TrueNAS will ID the failed disk by serial number. Drive letter changes when cabling changes.
To digitize LP records you have a couple of options. The Parasound Z-Phono USB from Audio Advisor. Pro-ject Audio also has a digitizing phono preamp. Both are good. Or a Schiit Audio Mani phono pre with a separate ADC. Schiit discontinued its ADC as it was not selling. The Parasound is decent. I’ve made transfers of some of my out of print LPs with it.
I would suggest that you put your preservation efforts into out of print titles that you love. I’ve found that many of the great 50’s and 60’s classical recordings are out of print on CD and not to be had for streaming. Most Bernstein, Ormandy, can no longer be had. And old London/Decca are out of print like the Benjamin Britten Curlew River premier.
If there is a modern remaster, stick to the Red Book CD. Often, especially with pop titles, the HD reissues are manipulated to impress hi-fi store style.
I missed that you had vinyl to rip.
As @David_Hamby says - save ripping vinyl for things that are out of print - because it’s quite a bit of hassle and only worth it where you need to. Buying CDs or lossless downloads is better value where recordings are available (if they haven’t been ruined by the loudness wars).
Assuming you already have a good vinyl phono stage you could consider the RME ADI2PRO - which is a very good DAC - but just as good an ADC - and will connect over USB.
I’ve been using one as my main Hi Fi DAC - and to rip vinyl for a few years.