Bose A20 users function question

[Let'sgoflying!]

When I have an external music source plugged into the A20 control, the atc audio does not silence the music, regardless of A20 switch position.
I have a half dozen other audio alerts built into the panel of this plane and none of them silence the music, except for the flaps in motion voice.
This I find mystifying.

 

[Arrow76R]

Perhaps the sound levels of those sources that do NOT silence the music are too low to trigger the Bose music silencing action. You might call Bose and ask if there is a threshold adjust for the silencing function.