Barry, I also use Volumio on RPi, but I feed an SMSL SU-8 DAC with balanced outputs before the Bryston amplification. I use several music services. Spotify when I want self-serve, and Sirius or internet radio for full serve.
In my opinion, the Spotify app is great and has an amazing implementation. You can stream Spotify through Volumio by enabling the Volumio plugin, while running the Spotify app from your phone, tablet, Windows or Mac computer, and bounce between them at will. Of course you can always just use Volumio to control Spotify, but the Spotify app is better. Unfortunately Volumio is not supporting Sirius yet. I hope that comes soon. In the meantime, I have an Echo Show 5 connected to another input on the preamp and I just need to say "Echo... play Seriously Sinatra" and I'm in business.
Sound wise, I have no complaints with Spotify, but have not compared it to any other service.