Yamaha DTXpress/DTXplorer/DTXtreme

I'm new to this list, new to the DTXpress, and VERY new to MIDI in 
general. I'm a drummer who finally broke from his purist thinking and 
decided to enter the world of triggers. So far so good. I have Ddrum 
triggers on my acoustic kit and everything seems to be working well. My 
question is this- I'd like to have a couple of my triggers run through 
the DTXpress and fire some sounds from my MIDI keyboard, but the manual 
is pretty vague on how to do it and so far I'm having no luck. Any help 
would be much appreciated. Thanks...

Kris