Questions about adding Options to the '04 Z

I heard a rumor that all '04 Z's are wired to plug XM radio directly into the unit without having to modulate the signal. Anyone know anything about this? I have a '04 350Z Roadster and want to add the XM radio. I was also wondering if anyone knows what it would take to add the factory GPS to a Z that did not come with it standard. Had the same question about adding the tire pressure sensors to a model that did not come with them from the factory. Any help is appreciated.