I've got a
DTXpress II, so maybe I can help a little.
The
DTXpress II has an improved brain on the original to start with. Then there's the pads - on the
DTXpress II, the crash cymbal has two zones to get different sounds by hitting different parts of the pad, and by grabbing the edge you can choke the sound. The bass-drum (or kick) pad is also improved, to allow increased sinsitivity and a double-pedal. The snare has also improved, as it now has 3 zones, to allow for clicks and rim shots etc.
Furthermore, the "frame" of the kit, its stand, has been improved and is now sturdier than the DTXpress I.
Hope that helps a little,
Ferdie