Humph, eight motor drives are for wimps, fourteen... that's more like it!
Seriously, why not just make a eight motor eight wheel drive, with the front and rear wheels raised a wee bit? You'd need a really high traction material to harness the power, which would wear down quickly, so you'd have to use wide wheels, but it'd turn nice, and be insanely powerful. Given, this can't push as much as a tank, but it will turn better. Or you could use a pneumatic pop caster on the tank treads... hmm.... where's that Bercoflex catalog...