Oftentimes when I wake up my MBP from sleep mode or reconnect the Thunderbolt hub, Apogee Duet stops responding to keyboard sound volume controls. When it happens, I can still change Duet’s volume from Maestro or Audio MIDI Setup.app, just not using the keyboard controls or OS X system volume slider.
I don’t know what causes the problem, but I figured out that I can make the keyboard controls work again by restarting coreaudiod via Activity Monitor.app:
or from Terminal:
sudo killall "coreaudiod"
Before finding this solution, I had been rebooting the computer to resume “the link”. Obviously restarting coreaudiod is way more convenient.
If this still does not work, you might want to try another solution posted by GearSlutz.com Forum user Sigfried Chicken. It used to work for me in the past.
If you know other solutions, please share them in the comments.