The Hyperion Duo is an awesome charger, and its expensive - but you're basically buying 2 high end chargers built into one charger. You could buy the 0610iNet and charge both at once with it - it has the power (250watts) - you'll need to figure out how to rig a balance connection so both lipos get balanced together.
The prob with running lipo in an Emaxx - the EVX2 esc has no builtin low voltage cutoff (lvc). If you run without lvc and drop batt voltage below 6v, you can damage the lipos. I've read a lot of sad stories about ruining lipos by overdischarging them - folks seem to think they can just stop running and avoid prob - I guess some do, but others don't and overdischarge their expensive lipos.
I have the older 3906 Emaxx, but have fully upgraded drive train to get it BL ready - I get 12-15min running 4000mah NiMH. I'm going to convert it to run a pr of NeuEnergy 2S 5000mah lipos with a Novak 2S smart stop lvc. I expect a 25% increase in runtime in converting to lipo - thats what I've seen with the smaller scales that I've converted.
This is good for some questions and worth a read -