FWIW, I experimented a bit and found that renaming monitor -> outputs breaks
   "audioctl -w play.gain=X" (again). I now commited a slightly different version,
   that allows you to turn off the internal (mono) speaker via
   
     mixerctl -w monitor.mono=off



ah!! that would be why i never commited a similar change i had in
my tree for a couple of years (and removed earlier this year.)