On the GTP I have a stock delco with CD head unit. For which I added a cassette player unit in the glove box so I could tap in the audio line as an aux input.
I just did something similar to the monzoon head unit on the Trans am:
How you can add an aux input/mp3 player without an adapter - LS1TECH
The difference is that you don't need an external cassette player and you just tap in the CD line within the head unit. I never took appart the GTP unit and I was wondering if it could also be done on the Delco GTP stereo. Has anyone tried doing it like that?