Would twin brushless setup with dual MMM's work withmy set up?

[_paralyzed_]

If you are stuck with 6s and the MMM your last setup seems to be the way to go. You may be near the limit of the MMM.

I'd go for a 1600/kv ish 1521 (or even 1527, go big!) and a 12s plane esc. They have drag brakes, your vehicle will stop! The CC HV110 is the boss, but a hobbycity "turnigy" unit has been proven to work well.

although the braking requirements of the ISC may not be met.

With 6s you'll really be pushing all of the components.