I'm about to do this but am just going to buy new as they are only $35 for the 3 B+ and not much more for the 4. Going to get one of the HiFiBerry Digi+ HATs, basic case, and power supply and feed the coax out to my Onkyo P-3000R preamp. I had thought about using a little Liva Mini PC running barebones Windows 10 but not sure I want to chance the USB output on it. The little Raspberry setup seems like the best bet to grab the FLAC files from my NAS and just use my Android phone, or one of two older Samsung Tab 8 tablets I have, to access the files via Volumio. Just trying to keep it basic.
I might also try casting those files from the Gizmo app on my phone to the ChromeCast Audio I have tied into the Onkyo stack, first, and see how that pans out. It sounds great currently streaming Amazon Music HD to it....very happy with that.
I have an extra Pi 3B v1.2, and two extra Pi Zeros V1.2, an extra Hifi Berry DAC+ Zero 1.0.1, and an extra HifiBerry DAC+ 2.6.
The 3b and DAC+ 2.6 I used for a bit in my streamer with moode and volumio, iirc. I may have tried other distros, but I can't recall specifically.
I don't think I ever powered either of the zeros up, one is still in it's original packaging. I also have an extra case for the 3b/hifiberry, I don't know what brand, it's two piece, metal, and worked pretty well as I recall.