Unless the Mini Commander EX firmware has been updated, you may want to consider a different option. Various folks had issues getting the serial data to function properly with those in the past. I haven't used one in years for the same reason. I'd wait for some current information on whether this unit is fully functional now. Personally, I buy something like an RCDR from Lionel for dummies, similar sized board, but I know the serial data works 100% on those.
As far as the diesel sounds, you can add a switch to the RS Commander to turn off the background sounds (prime mover, etc.) and only get operator triggered sounds, i.e. the horn and bell. Even without the switch, you can simply use the remote and turn down the background sounds independent of the horn/bell sounds.
