Alex, Those planes don't have retracts, brakes flaps...blah blah blah, so you'd think a 6 channel is OK, and it is, BUT those airplanes can have 2 to 4 servos on ONE aileron.

Guys flying that kind of equipment need an airborne power supply to feed those power hungry servos. A Power expander like Power Box and the like is what is in place between the RX and the servos. These 'expanders' can split channels to give you "more RX channel ports" while using the basic 6 or 8 channel RX.