This applies to the Legacy Saffire Units
Hardware control is a feature which allows the MONITOR knob and DIM/MUTE switches to be linked to the SaffireControl and SaffireControl PRO software. This can be turned on in the SaffireControl/SaffireControl PRO software for any output pair by pressing the 'H' button for that pair.
In order for the hardware control MONITOR knob and DIM switch to work, SaffireControl/SaffireControl PRO must be running and hardware control must be turned on.
Note that the MUTE button will function whether SaffireControl/SaffireControl PRO is open or not.