Pi's can also be used as servers and receivers for the open-source Logitech Media Server software. I've been successfully using it for synchronized multi-room audio. It has support for both local music and streaming services.
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.
Squeezeboxes are rather durable, probably will use those for many more years. Have been also collecting little replacement player stock :)
Wanted to evaluate esp32 -based player mainly for hacking purposes, but havent found yet time to work on those.