I have every format you could mention. The vast majority of it is FLAC ripped from my CD collection, but having been building up a digital collection for nigh on 20 years or so now (wow, that makes me feel old) there's everything from MP3 to DSD and MQA in there, so it's not the format the music is stored in that's the problem.
I have been doing a bit of experimenting this last week or so with the Pi and replaced the Roon bridge SD card with one running Volumio where I then attached a backup hard drive with all of my music on and played directly from there - That sounds really great. Tellingly, I also tried mounting the drive the music is stored on via the NAS setup of Volumio so that it's playing over the network as Roon does, and that went back to sounding lifeless again - so I'd say that it has to be either the network or the server but given that playing via Spotify Connect or internet radio sounds great, that points the finger quite solidly towards the server for me. Time to start a bit of server tweaking I think.
I also have an old Mac Mini that's not doing anything these days, so I could try installing Roon Server on that and see if it sounds any different...