Yamaha DTXpress/DTXplorer/DTXtreme

Hello,

I have owned a DTXpress II kit for a few years. I would like to use my
software drum synth on my PC over MIDI. I thought it would be as easy
as connecting a midi cable from my DTXPress II module to my PC midi in. 

Unfortunately not. There is no MIDI signalling whatsover coming out
from my DTXPress II MIDI out jack. I have the switch at the back set
to MIDI.

The PC synth works fine when I connect a MIDI keyboard to the same
input, but my DTXPress II gives nothing out through the same cable.

Help!

br. Timo