As a current sirus subscriber, I would like to have the option to use my service with the stock OEM head unit vs. a plug n play reciever. Looking on the mazda webiste it says all SPEED 6 units are "compatible" with Sirius. Does the optional, $400 add-on include the tuner...or just the activation and 3 mo. subscription. Or is the Tuner already integrated into the OEM headunit?....I can add another reciever/ tuner to my subscription for a minimal amount and dont want to pay extra for a second reciever if its already in the vehicle.