Hi Dan what a great idea , if you have a set of Tamiya DMD/mf in the drawer but it has the wrong sounds ,great way to change the sounds and save buying another set of DMD/MF units . I do have a set of Sherman units not using them as yet but this gives me more options.
Have you ever tried to make a recoil for the Sherman DMD/MF , If you have the Spektrum DX6I it should be possible to operate a servo recoil if you fit Fire buttons to the radio , all you have to do is mix the 5th channel which you connect the servo to the fire on the DMD/MF .The theory is correct not sure how it works in practice.

regards pete