I originally used the stock head unit and an FM modulator with XM. Compared to CD qualtiy I was severely disappointed.
I went ahead and changed the head unit with a JVC with an AUX input on the front of it. The sound difference is beyond words. The difference is huge to me. The sound...
Yeah, the idea sounds pretty lame, but if someone (like myself) is trying to hook up XM while keeping the stock HU it is about the only option.
However, I've heard very good things about the sound quality when hooking it up this way.