Hi David!
I recommend using the Special Edition sound set for this device and reserving one program/channel for the piano and two for the organ. To change the registration of the organ, please use keyswitches and MIDI CC commands. Here are two examples.
~N26,10 (sends keyswitch D1 with velocity 10)
~C1,127 (sends CC1 with value 127)
I hope this helps.
Best,
Andi
Vienna Symphonic Library