Our CX-7 is Sirius XM 'compatible' apparently (button on the dash, antenna, etc.). What further hardware do I need to install in order to subscribe and access satellite radio?

I didn't get ahold of the parts department at our dealership, but the service people said it was going to be $270 just in labor. I've been researching installing the after market adapters, and if it is anything like that then I will surely do it myself.

Thanks.