Bummer, dudes. The Peripheral Electonics (aka PAC) ISGM74 does NOT work with the 06 Pontiac Grand Prix GXP Monsoon with the 6 six changer, XM, and Onstar. When I plugged it it, it didn't even recognice XM bands (even through I only get the intro channel). It goes back to Best Buy.
The IPOD Nano is pretty sweet, but without an interface into the radio, it's just useless to me. It might have to go back as well, until I find a better solution.
***** UPDATE ****
OKay, I'm going out tomorrow night and hook it up again, and play with it some more. Maybe I'll leave the XM plug out, since I don't use it anyway. I've also sourced another unit, the Soundgate GMPD2 which claims to work on my car. If I don't have any luck with the ISGM74, I'll look into that one.
