Thanks, Ralph. I wish that it did work that way.
I have a PS Engineering 501 intercom and am running from the ifly to to the aux input (now with a ground loop isolator to reduce noise). The intercom does reduce the volume of incoming muisc on the aux input when anyone in the cabin talks on the intercom, but does not mute it. That lasts for only a few seconds and it returns to normal volume. The main problem It also doesn't reduce the volume at all for sound incoming from the radio. So the music happily continues while ATC is talking. The 15 seconds it takes to get to the music app and pause the music is a long time under those conditions.