http://www.infinitipartsusa.co....html
http://www.midwaypartsteam.com/MC-DFG-CBG.aspx
Here are some Satellite units from our sponsors.
However, in reading your post, the dealer seemed to infer that the satellite unit was already installed. Fist you'll need to confirm this. The XM or SIRIUS unit is usually installed to the left of the spare tire in the trunk under the false floor. You're car would likely have a sat antenna mounted if it has this as well. If the unit is there, you only need to activate it. If not, you'll need to buy one of the units I linked to above along with a matching antenna. The AAI-NIS2 is an aux adapter and is different from the satellite. It allows you to plug into the satellite radio connection on the back of the head unit allowing you to input an auxilary audio source(ipod, mp3 player, game console, carputer, etc). It is not needed if you want satellite. you can have either a satellite tuner installed or the AAI-NIS2, but not both at the same time as they use the same connection on the head unit.
If your car is prewired for XM or SIRIUS, you only need to plug the satellit unit in on the plug at the rear to install. It's a pretty simple install from what I've seen if the car is prewired.