Yea, I've looked at that diagram...that's how I got that pin info above...but the diagram that lists what the pins are, is incorrect. I lists only positive leads on the right speakers, and only negative leads on the left, etc. Its showing both front and rear channels coming from the stereo, as well.

What I see from looking at those diagrams, however, is that the left and right positives and negatives go back to the amp, and are doubled before they get there, so that the amp gets two left positives, two left negatives, two right positives, and two right negatives.

This makes me "ASSUME" that the 4 input channels on the amp correspond to the 4 output channels on the amp (a front left, rear left, front right, and rear right), and that we are just feeding both the front and rear with the same signal from the two channel head unit using the doubled wires. With a four channel head unit, why not send 4 channels to the 4 channel amp, and on through to 4 channels of output? This would allow fade to act as a bass bias adjustment of sorts, giving you independant control of the subwoofers.