An Elevon Mixer will work fine with a four channel transmitter. And yes the Y adapter as well will work. I used an Elevon/Flapperon Mixer on my Goldberg Extreme 330 using a Futaba Skyport 4 channel transmitter. The channel six slot is just to supply additional power for the mixer to operate both servos. And then the Elevon Mixer receives transmission from the aileron control (channel 2 most likely) and supplies that same signal to the other servo in reversed direction. We recommend this device to lots of new members at our flying field who bought a 4 channel transmitters and a plane requiring 2 servos for ailerons.