So you have the 3 power connectors? (P7, P9, P10) along with all the others (Control, Key, service, sound, monitor)?
If so, a 2-board will also work. It just does not require the P7 connection to the sound board since the sound board is on one of the two boards.
I went through the same thing, but I can plug in my DKJr 2-board and my DK 4-board into an upright.