Alright,
I had the time to address some more feature requests.
Version 0.7.0 just made it to extras-devel and adds:
- an option for enabling auto rotation,
- a counter for the trigger,
- and a setting to select a monitor as source.

The auto-rotation option is quite straight forward.
Even though, I actually don't know why you'd want a smaller display.

The counter for the trigger is useful if you do not want to execute a command just when the threshold value was reached or exceeded once but you want to make sure the threshold value is reached/exceeded some 'n' times in a row.
Currently, the audio data is picked up with a frequency of 25 Hz, so if you want to trigger a command when the threshold was exceeded for one second you'd have to set the count to 25.

Last but not least, the "Monitor" source basically picks up the sound which is actually played via the speakers, so you can "measure", e.g., sound files you play.