If he has a Sirius account, it has to be a Sirius radio. Sirius and XM are practically one and the same now, but the radios are still different. You'll need a car kit to put it into your car --and I recommend getting it professionally installed. Don't use that cassette adapter thingy -- get it wired directly into your indash receiver.
I've been a Sirius subscriber for more than 2 years now.