If you'd rather have SIRIUS Satellite Radio, you don't need a new headunit at all.
SIRIUS is releasing a SoundGate adapter that uses the factory headunit.
So all you would need is:
Of course, each of those items need installed, but you'd still have the factory headunit. ...just another option.
I believe you can find more information about this on the www.siriusbackstage.com
Oh, and I'm in NO WAY affiliated with SIRIUS Satellite Radio. But I do love it to death! Long live the Dog-Star.