Ok, XM and Sirius do not share components... so the tuner and antenna would not work at all for sirius... they work on different frequencies and slightly different systems... plus the antennas are configured to recieve the signals in different ways....... so for the antenna, you could probably swap the guts of a sirius antenna into the stock XM antenna housing and run the new cable to the new tuner you would need. As far as changing the tuner and retaining the stock controls, thats kind of a hit-and-miss..... they do use a seperate tuner unit.... but as far as getting the OEM deck to control a sirius tuner, who knows.
Now that that is somewhat covered.... why do you want sirius instead of XM? just curious..... its probably not worth the extra hassle and expense... as you'd have to buy the new tuner and antenna... plus whatever would be needed to make it work... then sirius is like $14 a month, and XM is $10.