You definately came to the right place, I doubt there is another collection of people you will find that have as much experience with large scale brushless conversions and setups as you will find on this forum. Now please trust us when we say that the 7700 motor is not the motor you want to use in an Emaxx. The esc is solid, but it needs to matched up to the proper motor.
From the Castle creations website:
NOTE: The Mamba Max Power System is NOT for use in 1/10th scale monster trucks. Who ever told you you could use a 7700 in an Emaxx is horribly horribly misinformed, sorry to say. If it was the LHS, maybe they can take the motor back. Maybe not used tho. If you think about it, its a "1/10 scale" system, but a 1/10 Emaxx is heavier than a 1/8 scale buggy. ;) A decent BL system for a Maxx sized vehicle needs to be ~1500W (~2hp.) To do this on 2S Lipo would mean an amp draw of around 200A+, twice what the esc is rated at, and far more than a 7700 sized motor could handle.
Really, the best way to go w/o dropping a huge amount of cash on a high end motor like a Lehner or Nue, is to get a Feigao 7XL or 8XL and run it on 4S Lipo. You will have a very fast and reliable truck, over 40 mph. I have a 8XL, and would personally recommend it. Mike has then for $90 IIRC.
Lastly, to do this you need to disable the on board BEC and run a Rx pack or buy a external BEC. External BECs have caused alot of glitching for me, so unless you have a digital radio like a Spekrum, I would try a Rx pack first to get things working, then play with a BEC from afterwards. Also, with a good BL system, you will never need 1st gear either lock the tranny in 2nd (easy) or get a single speed conv. from Mike (easy too, just extra $.)