Nymphcast looks promising. Otherwise for the sync there's stuff built around snapcast. It has the fundamental limitation that it's a dumb pipe. You can control

Nymphcast looks promising. Otherwise for the sync there's stuff built around snapcast. It has the fundamental limitation that it's a dumb pipe. You can control the volume and mute it, but a pause only happens when the snapcast gets to the silent "paused" part of the buffer. The sync does work very well though. Maybe something will be possible with pipewire?