I don't know, same thing in the EDGE and S80, only reason why we even listen to it is because it's free, or was. This was all last year when we first bought the cars.
It just had horrible reception in so cal, the slightest thing would make it cut, trees, little stuff, our XM kit (bought at Target, not intergrated, the sportscaster) in the Audi on the other hand, nearly never cut, even under overpasses and such.
I still have my handheld XM radio and it's awesome, I can get an ok signal inside my house.