if the JVC headunit is Sirius ready (as you stated), all you will need to buy is the SiriusConnect for JVC (Model#: SIR-JVC1)
here's a link to one on Sirius' website.
they're very simple to set up... literally just plug and play. run the antenna to where you want it, and then the brain can be tucked away somewhere under the dash, and that's it. from there you'll need to switch to the Sirius band on the headunit itself, call up Sirius and they'll walk you through the activation.
before you call Sirius, make sure you know how to locate the Sirius band on the headunit... my brother got the samething last year, but it was for his Pioneer... it took me a few seconds to figure out how to switch to Sirius on his pioneer..