RE: lipos for rx power
I don't know about the RXs taking a 2-cell Lipo, but I kind of doubt it will work.
Just as importantly, most servos can't handle that high of a voltage either, they get all jittery, or something burns up.
Everyone that I've seen using Li batteries (including the Li-Ion packs I have) use a regulator of some sort to drop the voltage down to 6v or less.
Keep in mind that a fully charged 2-cell Lipo is going to be a hair over 8v.