I've built something similar at home with three RPis and Snapcast [0]. It has an integration with Librespot [1] that shows it as a Spotify destination. It works

I've built something similar at home with three RPis and Snapcast [0]. It has an integration with Librespot [1] that shows it as a Spotify destination. It works really well! [0] https://github.com/badaix/snapcast https://github.com/badaix/snapcast [1] https://github.com/librespot-org/librespot https://github.com/librespot-org/librespot