RE: multiplex evo 9
Sounds like you are trying to mix in the wrong direction. You want to mix rudder to aileron, and rudder to elevator.
The basic rule for mixing in any Multiplex is to look at a control surface (or servo) and ask what controls do you want to have an affect on that surface. In this case you want aileron servos to react to aileron control and rudder control. So create a mixer that has aileron and rudder as inputs. The mixer can have other controls as inputs even if not used on a particular model, they just get switched off on any model where not required. You could add rudder in to the existing aileron+ mixer or make a new mixer with aileron and rudder inputs. Then you assign the aileron servos to that mixer. Note that in the Evo to get rudder to make two aileron servos behave as ailerons you need to assign the full rudder control in to the mixer, not rudder -tr as you might expect.
Do the same for the elevator servos. Have a mixer with at least ele and rudder control as inputs, then assign the ele servos to that mixer.
Finally go to the mixers menu, select the aileron mixer, select each control in turn and set the amount of travel it makes at the servo. Do the same for the elevator mixer.
H.