Sir-GM1 - '04 SRX AWD w/ Nav - Bose

I just purchased an '04 SRX AWD with factory Nav and Bose. I also purchased the SIR-GM1 as I want to receive Sirius via the factory system, but I am not certain if I have an XM ready unit (I don’t see any buttons or digital displays that reference XM). How do I know if my head unit is XM-ready? There is an antenna located inside the windshield above the rear-view mirror, although I’m not sure if it’s a Nav or Sat antenna. With all of this said, I'd like to be prepared for any eventuality during the installation process. I read a thread from several weeks back that mentions the possibility of adding pins, but I'm not sure what that entails. I'm somewhat mechanically inclined but I am not an electronics expert by any stretch of the imagination! Could someone explain & and can the average Joe do this? Thanks to all of you in advance for any words of wisdom you may have for me. PS. LOVE the SRX, and I'm sure I'll never want to part w/ it once the Sirius is installed!

Thanks!
Mike