ORIGINAL: Hill202
Why can't I just plug the 2 a123 batteries and 2 switches directly into the rx?
You can and most do. I run 9 Futaba 9157s through dual 6014 Futaba receivers. Running your power through the receiver will not cause a brown out to the receiver as the receiver is merely a bus for power, no different than a battery connector.
There is a long and very detailed build thread on the Beast in the Leading Edge forum over on F-L-Y-I-N-G G-I-A-N-T-S. Get a good switch like a Wolverine switch with dual input and dual output. Leave the NiMh batteries back in the last decade and move up to A123s.
You'll love the Beast.