I’ve experimented a bit with my new Raspberry 4, and have found a very nice little minimalist setup with surprisingly good sound quality and excellent Roon integration (except DSD which I don’t bother with):
Install piCorePlayer 6 beta (downloaded from here: https://repo.picoreplayer.org/insitu/piCorePlayer6.0.0/piCorePlayer6.0.0-Audio.zip) on Raspberry 4. Please note that the official version 5 does not work on Raspberry 4.
Configure piCorePlayer, which is done on the IP address for Raspberry 4.
Turn on Squeezebox support in Roon and play. There are also players for smartphones etc. The support from Roon is perfect, almost no delay and no “pops” or other noises.
piCorePlayer (or really Squeezelite) supports up-sampling with SoX, and all parameters can be specified. In addition, it seems extremely efficient, probably because they have expanded the kernel in the OS with support for audio functions.
I’ve configured my piCorePlayer like this (all done via webpage at Raspbery 4’s IP address):
Up-sampling according to something that John Swenson liked, gives a spacious and soft sound. The argument is “mI:::28”. Also try what Archimago suggests here: https://archimago.blogspot.com/2018/01/musings-more-fun-with-digital-filters.html which is more neutral and forward.
I have down-sampled the CPU in Raspberry 4, and set it so that it does not change frequency with “performance”.
I also turned off the power to WiFi and HDMI (using SSH / Putty to log into it), to make Raspberry 4 as interference-free as possible.
The result is a surprisingly good endpoint, with quality up-sampling, for virtually no money. And if you like, attach some USB tweak (preferably something that replaces the VBUS power), to get another level up in sound quality (personally I use this https://www.diyinhk.com/shop/audio-kits/111-xmos-192khz-high-quality-usb-to-spdif-with-ultralow-noise-1uv-regulator-wmanual-power-switch.html which is excellent). Can also be combined with so-called HAT (HiFiBerry, Allo Signature etc).
All in all it sounds really good, and with minimal load on the Roon core and about 5-10% load on Raspberry 4. In addition, piCorePlayer is free (another option is HQPlayer embedded for even better up-sampling, but that isn’t free).