Similar problem here.
I am using a nice USB DAC with software-controlled hardware volume.
Sound is top notch when playing files through Volumio.
Now on the AirPlay side, when adjusting the volume on the AirPlay source (e.g. an iPad), this doesn’t change the volume on Volumio.
It reduces the volume on the AirPlay source before being send through AirPlay.
Which is awful because it is purely digital volume (it reduces the number of bits the audio is encoded in).
I believe there is some change to be applied to Volumio, to be declared as some “AirPlay volume-controlled receiver”.
If you know Kodi (which AirPlay is not working that well), there is a setting to get the receiver volume control by the AirPlay source.
Any chance to implement this volume aspect in Volumio?
It’s just painful to have to put the volume to the max on the iPad, then move to the Volumio interface and adjust the volume …