I've been using Roon for a while but felt like trying Volumio.
I've installed Volumio on my Digione Player (RBi 3 B+ with digione board)
It is up and running and playing. I have a backup of my music collection connected (a western digital external HDD with no extra power supply). I've read somewhere that it is better to have an external HDD with its own power supply... Would that be better in my case too?
Or is this all I need? I maybe should use the Intel NUC that I used for ROON ROCK somehow?
I also wonder about Tidal and Spotify. What works best with Volumio and gives the best sound quality? I prefer Spotify but would go Tidal if it has clear advantages.
Yes, it is highly recommended, if not a necessity, to power your hard drive separately. A simple powered USB hub works. There are "special" hubs for the Pi that can also supply power to your Pi with a single, decent power supply.
As for the second part: Tidal and Qobuz are high-res streaming services, they will stream in CD quality or higher. Spotify (Premium) is limited to 320 kbps, which is much lower in quality. It depends on the rest of your set and how much you care about it if the difference is noticeable.