After my own initial frustrations & seeing others experiencing the same thing, I thought I'd throw in my two cents worth.

I set up my Tamiya KT & Panther with a DX6i using the following connections between the DMD & AR6100 Rx:

DMD Rudd to Rx Aileron
DMD Thrott to Rx Elevator
DMD M Gun to Rx Throttle
DMD Turr to Rx Rudder

Please note that I use the transmitter right stick for throttle & direction; left stick for turret rotation, main gun elevation, & firing the main gun & machine gun.

On the transmitter menu, I set them up as aircraft, & set sub trim throttle @ +60. This allows me to operate gun elevation by moving left stick half-way in either direction, fire the main gun by moving left stick full up, & fire the machine gun by moving left stick full down without having to move the trim slide.

Hope this helps.

Some additional info: After experimenting, I found on my Panther I can also slide the left stick trim all the way down, & set the sub trim throttle @+85. This also allows me to operate barrel elevation with half stick throw, while full stick throw in either direction will operate the guns. Don't fully understand how all this works together yet, but experimenting with the stick trim setting & sub trim setting seems to be the key if you want to fire the guns with the stick, which is what I prefer. As far as I can tell, there are multiple combinations of settings one can use to compensate for the differences between DMDs. My experience is that no two DMDs work exactly the same way.

I do have a problem with the DX6i however; I like the radio, but its memory is not large enough to hold all of my R/C projects. Guess there's another radio purchase in my near future.