Dava,
That does sound like a better proposition. After using the Nav for a whopping two hours or so, I think any relay/automuting would get really annoying as it tends to beep quite a bit in non-highway driving. I don't have a switched mute line from either the phone (Motorola installed hands free kit) or the Nav (it's an ipaq with an external GPS receiver), but I think I can make the 2" reach over to the stalk controller to mute or hush. Having the sound injected right to the amp would be great.

Where do I get (or how do I make) the impedance matching unit or ground loop isolator? It sounds interesting.

-Zeke