We use the Starmate portable plug-in radio with a dock in the truck and a dock in the fiver. The truck dock is plugged into the Aux input on the truck radio; the fiver dock is plugged into one of the Aux ports on the stereo amplifier that drives the surround sound in the fiver.
We have an "Ala Carte" subscription that gets something like 50 channels of your choice for $8.99 per month. Se have been considering dropping it since Sirius has cut way back on their NPR coverage this season - lost one of two NPR channels and lots of repeats on the remaining one. Too bad there is no competitor out there!
Streaming WiFi would be an option, but the cost would probably be more than the Sirius.