For split elevators and two servos I would use the DX7, as it lets you fine tune the positioning of the elevator halves.

Use the Aux2 channel and either mix 5 or 6. With these mixes the sub trim works on both the master and slave channels. Can't remember the rest of the detail (I'm at work!) but I have done this on the Dx7 a couple of times and it works well.

Can't help with the OBG, never used one myself either!

Terry