I am actually in the same predicament almost exactly the same time lol I have the DX6i and trying to do mixing using the throttle and rudder. I have managed to get it to go forwards and backwards using the throttle to rudder mix and 100% but cant seem to get it to mix the rudder control to the throttle to make it skid steer. I hope this helps a little for you Henry as i have it half working lol also would appreciate any advice!

Thanks everyone!