04 Edge radio issue

Ok, heres the deal.
I'm installing 2 Sony 12's in a 2004 Edge Ext. cab Ranger.
The guy has the factory 6-disc in-dash head unit in it, and he wants to keep it that way. It also has the factory "premium sound" which has a sub in the bottom of the console. My problem is, when installing the converter box that converts speaker signal to RCA pre-outs, I dunno which wires I need to hook to. I've traced the harness to where the subs are installed, and there are 3 wires per speaker..2 hots and 1 common ground. The little converter box I have installed has the connections for all of these wires, but I still cannot get a signal. WHen hooked like the directions say, the 12's are barely working. What do I need to do to get this going right?? I've installed many systems in Rangers, and I've never come across this problem.

Thanks alot to whomever replies.

I have a 2004 ranger with the stock pioneer sound system. its an amazing system to begin with. I put 2 10 inch kicker compvr's in the back of my truck and personally i didnt want to risk doin it myself and messing it up. I took it to circuit city and they had it done with in a hour, they give you a lifetime warranty and its soo much easier. 65 dollars. althoguh because i kept the stock head unit i had to buy a 20 dollar adapter but now it works amazing and i can set off car alarms, so def just do it professionally its worth it