I’m looking for some advice on what to upgrade next.
I have an i7 Intel Nuc running rock. Its housed in an Akasa fanless case and powered by Sbooster linear power supply. The OS is an an internal SSD and media is Qobuz extreme, I dont have any other media. The NUC connectd directly via USB to Mutec MC-3 for reclocking then to my audio note DAC.
So is there anything else I can upgrade or have i reached the end of the Roon journey?
USB cables
How does your music sound, what’s missing?
You don’t say anything about the most important component - the speakers.
All this digital stuff is, for the most part, costume jewelry, IMHO.
BTW - I’m an admirer of the Mutec 3+ USB. A nifty device.
How about upgrading to a „lifetime“, if not already?
Otherwise, enjoy the music 
I’ve just bought Audio Note AN-E speakers, Audio Note Soro SE Signature amp and Audio Note 2.1x signature DAC. I’m really happy with the system sounds just amazing, but if there is an easy upgrade then I’m interested.
Do USB cables really make any difference - I’ve never heard a high end one.
You really have to get off the upgrade train and enjoy your system for a good while, otherwise it never stops and one can become an equipment junkie instead of a Music Lover. Or is it too late already? 
Spend money on great music… Go out and see new live bands…
Yes they do.
Where are you based?
I live near liverpool in UK.
I’m surprised just how good Qobuz is - I have 3tb of flac and mp3 files - but I dont connect it anymore as everything I had is on qobuz plas a lot more and it’s all lossless.
I would try and persuade your local dealer to lend you a few cables to test out.
I’m a big fan of Audioquest, I think there is a dealer in Crosby.
You’ll find opinion divided on that one. Really poor quality cables can suck but there’s no need to spend silly money on USB cables IMHO
No, they don’t.
Here’s a couple of links that suggest there’s not too much to worry about regarding USB cables:
The only time I’ve noticed a difference the cable was clearly faulty, i.e. skipping in tracks. Oh, some USB cables charge devices considerably slower than others. I’ve only noticed that when charging IMR batteries though.
I use the lowest priced AudioQuest and BlueJean cables because I trust they’re up to spec and, IMHO, that’s all that’s necessary.
YMMV.
FWIW.
Not that I can hear.
Especially not since your DAC is not connected with USB.
The Mutec outputs SPDIF, right?
If a person is going to obsess, they will. Regardless of reasoning from others. I too would advise to enjoy the already awesome system you have.
BUT, if you have to spend money, ‘just to be sure’, another option might be running the system with the Nuc wired to your network, and an ethernet connection from the network to a Roonbridge>DAC. That is the configuration recommended by Roon (isolating the core from the endpoint). This also gets you off the USB cable jag, even though there is a USB (or SPDIF) from the Roonbridge to the DAC. A microRendu is an example of a Roonbridge. (You don’t mention your network configuration but I’ll assume the Nuc is wired to your router)
Given the quality of your system and how it’s being used, I doubt there will much of a sonic difference. Maybe if you squint…
Yeah, you’ll have Ethernet to a MicroRendu, which needs a power supply like the Uptone LPS-1, which in turn needs a power supply, and then a USB cable feeding the Mutec 3+, and an SPDIF cable feeding the Audio Note 2.1x signature, and audio cables feeding the amp, and speaker cables.
Plus the NUC and the Sbooster.
And an network cable to a network switch, and it has a power supply that you could upgrade.
Ten boxes, thirteen cables of different kinds plus six power cables.
And it will sound the same.