Not great news I'm afraid.
Just set this up, all devices on wifi. The amp is not connected to speakers, so is acting like an Ultra.
Yes, 100% volume. I'm in a 13m2 room and it's still far, far too quiet with the gain at the default of 0.
Increasing that on each Sound to +10db fixes it somewhat, but it's hardly cinematic.
"The Beekeeper" (Jason Statham!) is humming, not buzzing angrily.
I have the group audio delay set to 70ms to make the lip sync acceptable.
Except the sound simply isn't in sync. I can clearly hear the audio drop out on one speaker or another very often, and just as often there's an echo as one speaker "says" a word then the other one says it afterwards. And I do mean afterwards. The entire word is heard on one speaker before it starts on the other.
Sorry, but I can't recommend you steer clear from this setup enough.
I have no such issues with playing music to the amp and grouped Sounds.
The volume is much, much louder and the music stays in sync. I'm attributing this to the 800ms group delay for the amp's wifi input, which cannot be altered.