The BK-9 sequencer can send sys-ex. If there is particular code you need to send to the SD-2, you can send it with this. Doesn't matter what kind it is.

But essentially, one sort of expects that the SD-2 is a sound bank, and I am not sure why you'd need to blow sys-ex at it? Primarily, you need notes, and controllers, and you are good to go, surely?

The trick is to get the master arranger to decide which Parts get played internally, and which get sent via MIDI, right? That's a snap for the BK-9.