2007 Satellite radio feature

Ive been looking for more information on how exactly this works but I think I am confusing myself. I own a 2005 , i replaced the stock radio with a 2007, but on the new radio it says satellite. I believe I read somewhere that there was a module to plug into the back of the 2007 radio to make the satellite button work allowing me to use xm/sirius, not sure which, through the stock radio. I cant find this part which leads me to think I have it all wrong! Little Help!

This might be it.

http://www.ebay.com/itm/Subaru-Legac...d75c1a&vxp=mtr

Part number: H621SXA000.