Dual trannies and 6W steering? Sounds like a nightmare to me, not to mention the large amount of batteries it will take. The center set of wheels would have to be stationary (no steering), just use the F/R to steer, otherwise steering would be difficult at best to do.
I've been wanting to do a rig style setup with dual drive wheels in the rear. Would be nice if someone would make a diff case where there was a spot for the pinion gear on the front and rear...
A guy over on traxxas was doing this, I have a link to 1 of his projects but he took all the PICS OFF !!! it had like 8 wheels and he cut diff cases in 1/2 and just glued them together and threw the pinion on the other side and something else, but he is the king of adding tons of wheels he did a few different ones im sure would come up with a search.
I thought about doing this once before. I emailed FLM and they said they could make a custom combo bulk that would allow a pinion to be on both sides. It is on the expensive side, they said $150 if some one else wanted one, they would probably lower the price if a couple of us bought one.