About a yr ago I bought a used Emaxx which wasn't running. I've been through it completly and it's currently running on upgraded S600 motors on 7 cell pacs (16.8v, less than 4S voltage). You're going to have to plan on driveline upgrades. Mine has destroyed the centers and once those were replaced (UE titanium and UE cups), I've started twisting wheel axles.
I'm guessing that after I upgrade those to 3.3 style cvds, I'm going to have diff probs.

The setup you're talking about is way more power. You need to plan on driveline upgrades, or plan on a lot of downtime waiting on parts. I'm building a new Emaxx based on FLM ext alum chassis, 8xl, Quark125b, flm hybrids with UE 6 spyder diffs, GM single speed, UE idlers, 3.3 cvds, and GM race suspension. Reading here, was apparent was going to be way expensive to run powerful bl in stock emaxx due to needed upgrades. I would consider selling your current Emaxx and getting the newer one and make it brushless. Its better suited to handle it and will cost less in the long run.