It's a convoluted setup I'm not sure I'd recommend to anyone else! :) Still tinkering on it, but current rig is a Respeaker Core [0] running voice2json [1], which sends MQTT commands to a Mac Mini running mopidy [2], and the audio is routed through Airfoil [3] to multiple AirPlay speakers. (In theory, a Pi could drive all that directly, using shairport [4] rather than Airfoil.)
The major shortcoming is that Airfoil doesn't support Airplay 2, so it doesn't take full advantage of HomePod stereo pairing; and while the sync is perfect, it comes at the cost of massive lag (5+ seconds). Sounds great though!
The speakers sync perfectly with each other for pure audio, but the setup is definitely unusable for video or games due to the sync delay. It seems to work okay switching back and forth between AirPlay 1 and 2, so I can temporarily take over from Airfoil and use them as an AP2 stereo pair, in which case they sync well for video.
Supposedly Airplay 2 was cracked about a year ago, but there still aren't any usable third-party implementations. Really a shame that Apple hasn't opened up the standard.
