John,

When
I plug one of these into the input jack of the intercomm, I have to
crank the volume on the player up to maximum and it's barely audible
over the background noise in flight.


Are we talking about the Garmin 340 audio panel? That's a known problem
- and there's a work-around and a fic by Garmin. If you're interested
in the details, I'll provide them.

Also, yes, this can be a problem.

--
Thomas Borchert (EDDH)