I think Mac is on the right path. You might try to filter as much MIDI as is possible from the master keyboard, aftertouch, pitch bend etc., and just have the notes of the needed channel alone go down the pipe. If that MIDI cord worked fine for other setups, it's going to work fine here....

The other thing you might try to do is record a short piece from the Nord into a computer sequencer, and take a look at the data in a list format. I don't know about the Nord, but I have had problems from time to time with other B3 clones sending all kinds of ultra short 'key bounce' notes as well as the main note. Organ keybeds are setup to trigger at the TOP of their throw, rather than at the bottom. This makes for a very quick response, and mimics the B3 keybed, which triggered a lot higher than pianos and other mechanisms, but a problem comes when the key springs back after you hit it staccato and 'bounces' a little at the top of its' travel. That tiny bounce is sometimes enough to trigger an ultra short note on/off that may confuse the Technics.

If the Nord is doing this, it'll be pretty obvious from the note list in the sequencer...