Yamaha DTXpress/DTXplorer/DTXtreme

I have no clue and would appreciate the advice and/or posts.

I have 2 sets. One with the DTX ver 2.2, and the other with the
DTXpress.I really want to upgrade the module, and I would like to stay
with Yamaha. But, I dont have the slightest clue what the differences
are. I am going to upgrade the DTX ver 2.2 to either a DTXPRESS II or
a DTXPRESS III. Those are within my price range($250-$350). Is this an
upgrade or am I stepping down? What makes the II or III better? I dont
think i'll go to the III because I believe its for 3-zone pads, which
I have none of. I really dont care for the user interface the DTX
gives me as oppossed to the DTXpress. Im told that their are more
voices in the DTXpess II..Is that true? Also, I would like to
interface it with my pc. I have found the DTX to be hard to connect.
My DTXpress hooked right up. Are their any other advantages to the II
or III? I really appreciate the input fellas. Thanks again.

Ern