they're usually always a seperate attachment as they do need an antenna to be run. however, the antenna can usually be hidden and still receive good reception. if you arent looking for dvd/nav id suggest this:
Amazon.com: JVC KW-XR810 Double-DIN Bluetooth Dual USB/CD Receiver with USB 2.0 for iPod/iPhone, and Bluetooth/Satellite/HD Radio add-on capability: Electronics
good reviews, has built in bluetooth, the lighting color can be changed (to match the amber in our cars), double din, and relatively cheap at $250. the XM/Sirius adapter is something like 50bucks as well..
since you have a base, all you would need is the deck, the satellite radio adapter, wiring harness, and antenna harness.