I am using this. LMS is running on the network. UI is material-ui (works great on mobile as well). Spotty as Spotify plugin.

I can play music directly from my mobile Spotify (so supports Spotify Connect). I can see all my Squeezebox players there, combines synced players flawlessly.

Also plays local files. And also directly from youtube.

I have about 9 players on different rooms and could not be more happy with the setup.

If you would like to know any specific details, just ask. Happy to elaborate.