1) Put LMS (https://lyrion.org/) on your home server/a raspberry pi.

2) Get a bunch of raspberry pi zeros with a hifi hat.

3) Put picoreplayer (https://www.picoreplayer.org/) on them.

4) Use the material skin (https://github.com/CDrummond/lms-material) so it doesn't look like 1995.

Congrats, you now have your own, fully open source, sonos equivalent for multi-room synced audio. Supports all major streaming platforms as well as a local library.