Isn't what you want to do to have four channels, and just change the rear EQs (RL and RR) to suit the rear speakers, and likewise for the front? OK, you're limited to five band parametric on each of the four channels, but each of those can be set separately and a five band parametric is easily equivalent to a ten band graphic if you spend the time to tune it.

To me it sounds like what you're trying to do is to get better EQ for the front and rear pairs by a clever combination of software and hardware changes. You're not asking for the left channel to physically come from the rear or whatever, yeah? Because the reality of the DSP is that it's delivered only two channels, left and right, and it then has two independent outputs (FL and RL, FR and RR) for each of those inputs. No amount of software mangling can change that.

Does that make sense?

Paul

P.S. I've got a couple of tracks on one CD that have a third '.1' channel encoded as the difference between the left and right signals - you wire a third speaker up to sit behind you with 'signal' coming off the left signal and 'ground' coming off the right signal from your ordinary CD player. I don't know if this changes the sound much, and I don't know if the theory behind it is OK or not, but there was definitely a signal there when I tried it a long time ago. It just didn't sound like much more than what was already on the left and right speakers...