Gents,
I have sort of the same problem here.
Using Airplay from my MacBook Pro (2015) connecting to my Denon AVR. Volume will be automatically changed on the receiver using the controls on my keyboard or volume control in the bar. Let's say these two are connected.
The problem is, just 1 block on my Macbook put's my receiver on 24 (Receiver goes from 0 - 99), if I go just on step up on my Macbook, my receiver goes to 52!!! So the volume is either too low or too loud. I know about the Option-Vol.Up control but this isn't what I'm looking for.
It's not app related, it happen with each app I use for music or video.
Connecting my iPhone by Airplay, it goes perfect! Like, volume half way up is more or less half way on my receiver. And this also with the iPhones of friends. I've already reinstalled my Mac, same issue. I'm on MacOS 10.12.2.
Suggestions please!!