I've looked into it several times since sat radio's inception, but never tried it. My understanding is that the SQ has diminished to the point of being unlistenable on something like axioms. A poster on HTF recently refered to it as "AM without the static". I like the idea of xm, but fear they've ruined it for people like us. Another potential pitfall is the proposed merger and potential future changes in reciever compatability.
I would get the pre-pro or reciever you like based on anything but sat radio. You can always add an outboard unit like the polk later.