Yamaha DTXpress/DTXplorer/DTXtreme

Hi everyone.  I'm new to this user group and really need someone's 
help.

Quick intro: Having taken up drumming at the ripe old age of 36 a 
year ago, I purchased a DTExpress kit partly because I live in an 
apartment here in Singapore and partly because I'm an 
incurable 'technophile'.  With a few additions, namely rack 
strengthening kit, DTXtreme snare (RHP120SD) with Hart 2-ply mesh 
head, two stereo cymbals (PCY80S's) and extra stereo tom pad 
(TP80S), the kit is a delight to play and great to look at.

Learning one-on-one with a teacher at a local Yamaha music school on 
a Yamaha Stage Custom acoustic kit, I certainly get the best of both 
worlds.

Finally getting to the stage where I needed to expand the kit a 
little further, I decided to buy the Yamaha UW500 Personal Studio.  
This provides MIDI connections to/from the DTXpress, inputs for a 
bass & guitar and a USB connection to a laptop PC.

Problem:  I cannot send a MIDI signal from the drumkit to the 
computer.  I formatted the laptop's C: drive, installed a fresh copy 
of Windows 98 SE, a clean install of the USB and UW500 drivers, all 
the switches in the correct position, plugs from in->out and out->in 
and channel 10 selected on the DTXpress, but something isn't right.  
When I connect a cable to the MIDI-out on the DTXpress, the MIDI-
>USB signal indicator on the UW500 just pulsates green indicating a 
constant MIDI signal is being transmitted through the USB cable even 
though I am not playing the drums (unplugging the MIDI-out cable and 
the light changes to a normal constant green).  Hitting a pad 
registers nothing on the computer.

Installing software such as XGWorks V3 Sequencer and S-YXG50 
SoftSynthesizer and I can play music from the computer via MIDI-in 
into the DTXpress, but cannot transmit a pad hit back to the 
computer.  I downloaded Yamaha's StickMaster software from the 
Internet which allows some playalong practise sessions, but the 
software states that no input can be detected.

Anyone else had the same problems and found the answer?  I had a 
look through past postings and couldn't see anything.  I've checked 
the settings from each manual and everything should be okay.  I 
really need the help of someone who has seen this before.

I took the UW500 back to the shop and tried a different unit, 
different cables and two different DTX kits - a DTXpress II and a 
DTXtreme.  We even did a factory reset on all devices just in case 
the problem was caused by tinkering with the standard settings.  All 
suffered the same problem.

Help!