I want to play music when airplay mirroring is connected, but is seems impossible to do that, when airplay mirroring is connected I can't force audio out to speaker, because airplay mirroring will disconnected when I do that. I want to know whether audio unit is support airplay?
Yes, it does. I have an app that uses a low-level custom Audio Unit and I just tested it on my Apple TV and it works fine with both mirroring and selecting the Apple TV device from the MPVolumeView view.