I just bought a PI3B+ and Amp2 and I've connect some speakers in different rooms to both channels. I already set the channels to mono output, so that I don't loose something of the audio signal. Mono sound is fine for me in my rooms.
Well, but I've no clue about how to configure alsa directly that it works with two independent channels, so that I can use at least the website on one channel (along with Airplay ("bathroom")) and at least Airplay ("kitchen") on the other channel.
Thx a lot!