I know there are universal XM tuners that work on Sirius ready radios. Maybe Sirius makes universal tuners as well.

Did you get the XM tuner on your car, with the Antenna installed. I don't think the antenna's installed if you opt out of the tuner option. Umm I may be confused. Does it come with the tuner already and you have to buy the subscription.

Sirius Satellite Radio Tuner for Kenwood Satellite-Ready Receivers

Sirius Satellite Radio Tuner for Pioneer In-Dash Satellite-Ready Receivers

TERK XMDirect Universal XM Satellite Radio Tuner Box This one is an XM tuner that works on Sirius Radios