My 05 Grand prix GT has the Monsoon stereo 6 disc changer with XM. (xm is not used)

I currently have i lifetime Sirius subscription with a Sportster 5 radio on my windshield. I am using the magnetic sirius antenna right now.

Since the car has a XM antenna above the rear window, can i use it and extend the wire up to my radio. That way i can get rid of the magnetic antenna.

I want to keep the portable radio rather than use the In-dash radio.