Multi-output MIDI device disables volume control When creating either an Aggregate Device or a Multi-Output Device in Audio MIDI Setup and setting it as the default audio output device, the volume control is greyed out and locked at maximum intensity. Why is that and how can it be bypassed?
Whilst I'm not certain why the single volume control in the Sound preference pane is greyed out (or whether that behaviour can be changed), the only way I found to allow me to change the volume at all was to manually adjust the "Master" volume slider for each device in the aggregate or multi-output device.