Question [Q] Android media channels - what are they?

My question is - What are the media channels in Android and how to configure them?
The question is triggered by a problem I am trying to find help with for few weeks now and have no luck whatsoever.

I've purchased an Android based car head unit running 2.3.4 version. The unit works fine except one problem - I can't get Tomtom application I own to produce any sound.
I can have radio or music player work on background and when tomtom tries to issue an audio instruction the background audio gets muted as it should but there is no instruction. Also the background audio doesn't come back after the Tomtom instruction finishes as it happens on my Samsung SGS3.
Somebody suggested me that I might be not using the right media channel for Tomtom and this is what got me puzzled.
What are those channels and how to find their locations or get access to configurations etc. Is there an app which can run as a service to detect the audio channel called by another application?
I would appreciate any hint as I am not getting anywhere with the issue.
GT-I9300
Stock ROM, XEMC2
SD Card - 16GB class 10