Although trying the ESC didn't fix the problem, plugging the other battery in did. Although not ideal, I might be able to plug a small 2 cell 1100 mah battery into the b/vcc port. It weighs about 50 grams, but as of right now it the only thing that works. You were right about the receiver not getting enough power. Would a setup involving both batteries work, or am I better off removing the positive lead from both ESCs? I haven't noticed the servos getting warm, however I'm sure if I left them in their locked state, they would. As for a Multimeter, I do have one and can use it, but it's not a super great one.
OK my suspicion of the Rx arose from the fact that it has the ability to drive the servos directly from a 8.4 voltage source. In my mind, (somewhat small at times), in order to drive ordinary servos a form of regulator would need to be part of the Rx. I searched the I/net for any info but so far have drawn a blank.
Anyway in order to make the Rx fail safe and to protect it there would logically be some form of over voltage protection. My fears were that it would be a shunt or crowbar protection for rapid response and as such it is capable of pulling quite a few amps from the 5Volt rail if necessary. This action would drag the rail down and overheat the BEC in the ESC. It could even be triggered by a noisy servo. (one that generates voltage spikes).
If using 2 batteries you would definitely need to remove both red wires from the ESCs.
Now for the lightest possible solution.
Remove the 5 volt leads from both of the ESC connectors.
Rather that using an extra battery you can fit a UBEC directly into the B/VCC and connect the UBEC to the existing battery, (a little soldering may be required at the battery lead connection on one of the BECs,
OR
You can make up a "Reverse" "Y" Harness out of either 2 extension leads or an extension lead and the lead from a dead/damaged servo.
By reverse I mean a single male plug, (the one that a servo will plug into), and two sockets, (same as the standard servo plug).
Now reconnect the red lead on one of the ESCs and plug the ESC into the "Reverse" "Y" harness.
One one of the "Reverse" "Y" harness remaining leads remove the red wire, (this one plugs into the selected throttle channel).
On the remaining "Reverse" "Y" harness socket remove the WHITE wire. This lead plugs into the B/VCC port of the Rx. This should allow the ESC to provide power, (5V) to the 4.0 - 8.4V input whilst isolating the 5V from reverse voltage feeding of the Rx.
Before soldering and modifying try removing a white wire from an ESC and plug it into the B/VCC port whilst at the same time ensuring there is not red wire connection to the output Rx ports from any other ESC. If it works then the "Reverse" "Y" Harness will work for you and that Rx.
Let me know what you find!
have fun