Ok guys, I'm lost. Here's the skinny:

I picked up an '04 xFire and the factory oem Becker head was replaced with a Panasonic CQ-C8100U (50w x 4, am/fm/cd). It appeared the rear speakers weren't working.

I downloaded the stereo pinouts and the audio diagram from this site, then I tore into the xFire, removing the glove box and looking for the xFire amplifier which I understood was under the passenger floorboard. When I pulled up the passenger floor mat, etc., all I found was a huge aluminum box that looked like it had more to do with airbags and other circuits but not audio. (I should have taken photos in hindsight).

What I did discover was that only the Panasonic head front amplifier outputs were connected to the yellow and yellow/violet wires in the dash which seemed to match the audio diagram pdf found on this site. At this point being frustrated and tired, I buttoned the whole mess back up.

I went back to the Panasonic head unit and poked around all the sub-menus and found a HPF rolloff set to 135Hz so I disabled that and voila - the rear speakers started roaring bass. however, since only the front outputs of the Panasonic are being utilized, I have no way of balancing front to rear volume using the fader control on the Panansonic head unit. (Gee, is this a novel or what?)

I found an OEM xFire radio on eBay with pics and the rear outputs match the stereo pinout jpg I downloaded from this site further confusing me since I thought the stereo pinout jpg was for a separate amplifier under the passenger floorboard, but apparently that is NOT the case at all ???

So the question is: IF the amplifier circuit from the diagram on this site is actually incorporated into the oem becker headunit, what does that amp circuit diagram have to do with the actual speaker wiring and where (and what's the color coding) are the actual rear speakers? Further, are the rear speakers coaxial as well? Four wires to each rear speaker would indicate that: +/- pair for low end and +/- pair for high end.

If I can get a handle on this I could use the rear outputs of the Panasonic head unit thus enabling me to have a front/rear fader control (my lips to God's ears!)

Anybody got a good handle on this?