This SkyDock thing is probably the most pointless device created for iPhone, in my opinion. Basically, it is a car XM tuner, that cannot work by itself, but requires an iPhone/iPod to be plugged in it. Probably its only added benefit is that it will charge your iPhone while it's plugged in.
For your home theatre, just use an iPhone/iPod Touch (with or without a dock) connected to your AV receiver. Use the XM or WunderRadio app to get the XM online.