I am just pasting this from my post at the Astromech factory....no point typing it out 2 times...
I hooked up the C6C and adjusted the proper jumpers on the Scorpion. I plugged in the left and right foot motor wires (from scorpion to the C6C) and the picoswitch that plays my r2 sounds..and powered it up. I WAS BLOWN AWAY!
Not only does it work...it works GREAT!!!!!!!!!!!!!!! Very positive response...LOTS more power..battery life seems longer, range is good...no sign of interference through aluminum body...no lurching. ALL problems solved!!!!!
I didn't even have a single cable backwards or even need to recalibrate my foot motors in the scorpion (although I did to be sure). I NEVER get that lucky!

Ecstatic!!! I am going to LOVE only using ONE switch to power up the 2 12v batteries, and only having to charge ONE set of batteries!!!
Now the bad news...
I spliced my vex motor wire with a vex extension (cutting off both male ends) leaving me with a female end I could connect to the C6C. I conencted it..turned it back on, threw the dome on...and powered it up again.
Dome rotation is not working. The motor responds and the controls all work out (left stick turns dome) but that motor is struggling. It barely moves in one direction and the other it strains and pretty much wont move. My guess is the vex system was delivering more voltage to the motor...now that the C6C is working with 5v only..thats not enough for that Vex motor?
I was toying with replacing the dome motor with something quieter and larger anyways..and I do have a motor I bought for this purpose years ago. I attached a couple pics (see post at AF). I got it from Princess auto...I think its for a windshield wiper.
So...how can I add another small speed controller...with minimal wiring and no extra batteries?