Here's a response I sent to Shark directly. He uses an Atari ST for sequencing. So, parts of this reply will be irrelavent to some. But there is I thought you might find it useful, and entertaining:
After a little experimenting, I found bank 14214 program 15 is a blank voice. The MSB is 111.046875, which I don't think is possible as an MSB entry itself! The LSB is 0. And the program is 15. In Cubase VST for the PC, you can enter the calculated MSB*128+LSB as one bank number. Hopefully you can do the same in the Atari. This is what you need to mute the voice, but not affect the volume or pan which would also affect anything on the same channel on a different device. Just make sure you can select voices on the other device manually, not through midi like you must with the DJX. And set the other device to not receive program changes. You'll need to put the DJX first in the chain because there seems to be no way to make the DJX disregard program changes.
Here's something to try for fun, enter in the bank 14210, program 1. Play a note, do it thru the sequencer, with LOCAL=Off (Function 84 on the DJX). Any midi channel will do. Play a note. Do you hear anything odd? Change the bank number up some more. If it's like mine, all sorts of goofy notes, which continue to play, sound. Press different keys. Do you get different sounds from the same bank/program setting? Weird, huh!
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Hope you find this useful.