hey guys. i have a 2006 cobalt LT and i want to add a 12" subwoofer in the trunk. i dont want to get a new radio because i dont want to mess around and then end up braking something. i have a normal radio without the satellite radio thing. i already have two alpine type S speakers in the back (i think the stock front speakers sound good). i don't really know much about this =/ . Does the radio have an amp output? or would i have to get the signal from one of the back speakers? if i do, how does that work?

this is what im planning to get:
http://cgi.ebay.com/KICKER-VCVR12-4-...item53e1efbf4b

and this is the amp i bought: (hopefully its good)
http://cgi.ebay.com/NEW-VISONIK-800-...item45f383a35f

let me know what you guys think of what im planning to do please. advice would be greatly appreciated. thanks