So I have this on the way:

http://www.folcik.com/hi002.htm

Which will allow me to pull the faceplate off my G8 radio and replace it with a fascia and the remote display setup from my empeg.

But I want to keep factory BT and on-star. I have isolated the the audio signal from the BT/OS unit and confirmed that it works just fine when routed into (for example) the mic in on my laptop.

Can I feed it into the MIC in on the EMPEG and have it switch to that when the phone remote line goes hot? I know it (EMPEG) can mute, but will it pipe audio from the MIC?

I'd check the wiki but. um. yeah.