Nah, that doesn't work, as you'd need four discrete combinations while currently you have two (i.e. left & right).

You have the four corners - FL, FR, RL, RR. At the moment, FL = RL, save for the overall level from the fader. So you have left & right EQ. In your idea, none of the pairs have the same signal to them. FL != RL because of your front/rear EQing and FL != FR because of the whole stereo concept.

I think you're stuck with the five band, four channel combination if you want separate front/rear EQ.

Steve.