I can't get the volume to go past 75 when using Airplay. It's the only thing that seems to have that volume limit. Can it be changed???
The manual is 227 pages long! According to that airplay volume is set by the Apple sending device.
In playback using the AirPlay function, the sound is output at the
iPhone, iPod touch, iPad or iTunes volume setting level.
You should turn down the iPhone, iPod touch, iPad or iTunes volume
prior to playback and then adjust it to a suitable level.
So I suspect your problem is due to limiting, by having the sending device volume at an inappropriate level. As I understand it the Denon and sending device volumes are operative.