Yamaha DTXpress/DTXplorer/DTXtreme

I'm about to buy either a dtxpress or dtxpress II.  I've read that
the dtxpress II has 3 zone inputs on all the triggers, but I have no
idea what that means!  Do the pads feel any different between the 
two?  And. . .do you guys think it's worth the $129.00 difference 
between the I and II?  I think I know what the other differences are, 
but since you guys are the experts :), any help would be appreciated!

Aaron