Just an FYI, I personally didn’t hear any difference using DietPi (Although I didn’t try in my multichannel setup). So don’t feel like Ubuntu won’t provide excellent sound. With tested compatibility for compliant devices, and sampling control etc it seems to be the best option atm (at least with my setup).
Ubuntu server is an image and easy to install. I believe when I installed Roon bridge, I needed to install a few small packages, like: chmod, sudo?, trz, curl, once done Roon bridge installed perfectly.
When you try to install Roon bridge, following the Roon directions, Ubuntu will tell you which processes are failing.
Ubuntu/Roon bridge has been flawless for me. Rock solid, no clicks pops, etc.