I have both the XM unit directly wired into the display screen and a Sirius starbase unit mounted under the radio across the front of the former cubby hole. It is a direct fm modulater connection (no static)
I find the XM to have a far stronger signal with less drop offs. The Sirius will sometimes lose the signal around town. The sound quality of the direct connection is much better than the fm modulated one. The FM modulated connection has a more tinny flat sound than the direct connection.
I purchased Sirius after the XM to give me some more options when I sit in traffic. After listening to Howard Stern this week when I had a loaner car, I like Opie and Anthony better. The music selections are a little better on Sirius (early and later classic rock). XM lumps them together.
If you want a directly wired Sirius or XM unit, try looking at www/PriusXM.com (he has the Sirius units now, Coastaletech is still working on the Sirius units, but has XM) I have the Coastaletech XM