If i might suggest a couple of ideas...
I am building a king tiger useing a spektrum dx6i, dbu and an rx-18. I am not overjoyed with the rx-18 throttle response or lack of ability to handle stronger motors... i am very happy with the dbu however.

I have set up twin speed controls from a hobby grade tugboat for very precise motor control using the mixing of the dx6i, however getting good sound that way is a challenge...

How hard would it be to have your system work completly independent of the rx-18, directly from either piggy backing on the hobby radio servo outputs or running the servo leads from your unit into a hobby receiver and servo leads plug into your system out to the various destinations... turret traverse, barrel elevation, machine gun...
or perhaps the leads would tie into the electric motors on the unit moving the barrel or turret...

Just a few ideas i am looking for so i can build and add functions to my tank as budget allows with out saving a big chunk and buying el mod all at once, life keeps eating the el mod budget.

Thank you for considering my thoughts,
Jeremy