I have been involved with radio installations from Delphi. The XM and sirius are two different systems. Delphi will soon be offering integrated XM and Sirius satelite radios. (Currently we have a deluxe radio that works with an external optional satellite reciever and antenna. The receiver is similar to a cigar box in size.) These new integrated radios use a conventional AM/FM antenna as well as a satellite antenna for use with the radio.
For the aftermarket with either product, you can get a satellite reciever and antenna which is much more compact and portable. You can use it with any FM Stereo reciever because the satellite Unit rebroadcasts locally within the car. It can also be used in your house as long as the antenna has line of sight to the sky.
You can not change from on carrier to the other with the same reciever. At least I have not figured out how to do it. It would be nice have this feature reprogrammable in software. I expect at some future date, it will be possible.