The instructions with my twin star call for 18 mm up and 10 mm down aileron. I could get pretty close mechanically if I replace the aileron push rod and maybe the control horn, but the usual way is to have separate right and left channels. Right now I am using five channels just for the normal flight controls. I'd also love to add full span flapperons and maybe differential motor control.
I got the basic TS set up this past weekend and it hasn't flown yet, but everything is already set up. Aileron diff, expo, dual rates etc. and I have the extra channels I need for the head tracking.
I love my 9 ch Futaba for good reason, and I think I would like the 14 ch even better. Spend money once, and use for everything instead of getting an inflexible beginners radio that requires you to make each plane fit the tx instead of making each plane the way it is supposed to be and adjust the tx to include the requirements of that plane.
If I sound as if I don't like any other solutions I will point out that I have ten different airplanes programmed into my channel 19 Futaba and a couple in my channel 14 (club glider frequency) tx. I am not about to buy an el cheapo six channel low class non-computer tx that I can only fly with one very limited style of airplane. I may be spoiled but I am totally hooked on the flexibility of modern computer tx's with lots of extra channels.