When I first got the GTO, I started looking at an I-Pod connector. I couldn't figure out how to do it, so I went to Tweeter. They looked at it, and said the same thing...No Way.
Forgot about it for a while, but I hate the radio, and got tired of listening to the same cd's. (Always meant to bring new ones into the car...) So I just went for a Sirius unit. Don't want to get into a discussion of Sirius vs. XM. I like the Sirius content, which is a matter of taste (no, I'm not a Howard Stern fan), but went more for the unit.
Had a Sirius Starlite installed by Tweeter, in the storage compartment below the radio. It looks factory, and when the compartment cover is closed, you can't see the unit. Totally stealth. If I could figure out how to post the pix, I would.
I usually don't like anyone working on my car, but after speaking to the installer, I felt that he really knew his stuff. He did such a good, clean install, that I also tipped him. It's so hard to find good people. Trust me, it's worth the $75 to have someone install the unit who really knows what they are doing.
Anyway, looks great, sounds great, even with the wired FM modulator rather than a direct input. As you have already found out, there is no way to directly wire anything external into the crummy Blaupunkt unit.
As for EQ, I am using the manual settings, with the factory EQ off. Hate that rock, talk, jazz eq garbage. Everything sounds better now.
But the best sound of all is the throttle and exhaust...Makes my day.