I'd love nothing more than to be able to agree with you guys, but I can't. The sound quality on Sirius is terrible. Some channels in particular where I notice how bad it is:
Liquid Metal
Real Jazz
Lithium
Boneyard
Hair Nation
The most obvious thing that sticks out are the drums. Cymbals have that wishy-washy sound, and when there is a fill, it sounds like the drums are under water. To me, it sounds like I'm listening to streaming audio over a dial-up connection. I'd be very happy if the satellite-based music sounded like the Premium Internet stream. But, I doubt that will ever happen.
For what it's worth, I'm listening on a factory installed receiver. Everything in the car sounds great (CDs, MP3s via a USB connection, etc.), just not Sirius.