I know the TruTrak autopilot will interface, but not as well as Dynon's. On the Dynon certified side there are many certified planes flying with a Dynon EFIS and autopilots that are not Dynon. Most likely the interface in minimal. Your best source is going to be Dynon or a Dynon installer.
My advice is the same as @airguy. Sell the STEC if you already own it and get the Dynon servos. If you don't already on the STEC, the Dynon servos will be less expensive and integration will be simple.