Chass,
I think Bill is pretty correct there. From my experience I would say by far most of them, even should they have more than one arranger keyboard, don't want to meddle with MIDI intricacies.That is basically the reason for my thread and suggestio in the first place. By merely connecting the acc. sections of two arrangers in general you set the first easy step which for the great majority will be amply sufficient.
At least I experience on a daily basis how comfy it is to play the two arrangers (acc. section) from just the lower keyboard.

regards
John