RoadrunnerSTi

I'm a complete noob to audio... I'm planning on purchasing a AVIC Z2 for my STi. My questions are these: Is it possible to have and be signed up for XM Live Traffic Navi updates alone, and not have to pay for XM radio? Are there 2 seperate adaptors for each XM hook-up or just one for both? Do you get a discount for signing up for both? Thanks for the help in advance...