I've got an Alpine head unit in my truck, and boat. Both have the add-on modules (made by DEI) that are integrated with the Ai-Net connection on the back of the radio for Sirius. If you did the same thing, you could transfer the brain of the Sirius from the truck to the boat by just plugging in two wires and the antenna.

My .02 = Sirius

I had XM for one year. The channels on Sirius are better for my taste of music. They have more rap and alternative channels. There are also so great techno/house music channels if you're into that.