I have currently been listening to sirius on my D2. I just switched over to XM and purchased the Pioneer GEX-P920XM. My question is, can I just unplug the power cord and antenna of the Sirius PNR-1 and connect it to the Pioneers XM tuner, or am I going to have to used the XM supplied antenna and power cord?

I think that they are different antennas

The antennas are mostly compatible. You will lose some repeater performance using a Sirius antenna for XM though. The power is most likely different

Plug for power is different. You can cut the plug off and splice the replacment on.