FYI......

If you have an '08/'09 Armada or QX56, and you want to switch from XM to Sirius and....

your vehicle DOES NOT have Navigation:

You can order a Sirius receiver and simply swich out the receiver which is located under the dash just above the gas and brake pedal.

your vehicle DOES have Navigation:

You are stuck with XM! There is actually no XM receiver under the dash. The XM receiver is built into the AV control unit that operates the Nav, Bluetooth, stereo, IPOD, and various other functions.

Not a big deal to me, I love XM, but I know the question has come up many times over the last few months.