Duff, there are these metal "keys" that you use. You pop the face plate off and then slide these keys into small slots that will release the radio from the cage. You'll need to be able to fish the RCA cables and UniLink cable up to the back of the radio. The tuner itself can mount elsewhere and the antenna will connect to it. Then, the XM will be one of your source choices and you're set.
If you don't have the keys, let me know and I could mail you a set if you want.
O'
"Little Mascara 3"
2003 266BR,496 MAG w/Bravo III