Gus:
As far as I know, you can hook up the audio output of the 2820 to a third party audio control panel.
Garmin gives the 2820 user a choice of how they want the audio output from the 2820 to be configured: Either as amplified audio that is provided to a speaker, or as 'line out' audio that is provided to a secondary amplifier or switching system.
Where you might run into problems is with the microphone, if you plan to use the 2820 to control your telephone. The 2820 will only accept 'microphone input' on the audio in jack - it will not accept a 'line in'. However - if you plan on installing a third party audio control panel, chances are that you will likely hook your phone up to the audio control panel (with wires), not to the GPSR (via Bluetooth). So, I don't think the audio in will be a concern for you, but you do need to know that the 2820 only accepts microphone audio in - or Bluetooth audio in - for the purpose of the telephone, not 'line' audio in.
There is a bit of an advantage to hooking up the 2820 audio out via a wire, as opposed to via Bluetooth. The advantage is that if you plan to listen to music, you will get much higher quality sound via a wire than you will via Bluetooth. The Bluetooth audio output is limited to the frequency range 0 to 3 kHz, audio output via a wire has no such limitation, and is much higher fidelity.
Michael
ermmmm.... I take it you've already got babies to some other very fortunate lady.... 
