You've successfully tested setting `kAudioDevicePropertyVolumeScalar`+`kAudioObjectPropertyScopeGlobal`, and it affected only the stream volume?
I have not, I have only observed `kAudioObjectPropertyScopeOutput` setting my system output volume to 1.0 from a previously muted state. `kAudioObjectPropertyScopeGlobal` is a no-op for me, I just blindly assumed that it worked as expected at the time of implementation on hardware that does support it.