I cannot control the volume from Infuse through Airplay if Infuse is the first app I use when I start the Apple TV.
My Apple TV is always playing sound through Airplay. It stays connected to my Airplay Speaker (Sonos one) at every start.
However, when I use Infuse in first, the Airplay speaker works but I cannot not adjust the volume with the Siri remote.
I have to switch to another app like the music app, adjust the volume, then go back to Infuse and now I can control the volume.
Maybe a bug to solve in a future update?