rx leads - 3wire leads that plug into receiver
BEC - battery eliminator circuit, it's what gives your receiver power to operate, most every esc has one built into it. Disconnecting the red from the receiver lead plug disables the BEC. Having more than one esc providing BEC, especially if each one has a high amp rating can provide too much current to the receiver & may damage the receiver or other components plugged into the receiver.
Each Sabertooth barely puts out 1amp, so two Sabertooths providing BEC in series is not much of a concern.
To wire the 2x25, you can get servo extensions from hobby shop or oline or from junked servos to wire the screw terminals. Red is positive (middle wire), Black or Brown is negative (outer edge), and white or yellow or blue is signal.
On the Roxy esc, use a pin or tip of exacto blade to pry up plastic tab in receiver plug to pull red wire out, and tape it back on the lead wires to isolate it from grounding or shorting out. You could cut it out too if you were sure you would never use the esc for anything else but this model and never need the BEC.
ngward is what? an hour's drive west? if you're really stuck to understand this.
