Yamaha DTXpress/DTXplorer/DTXtreme

Im confused about the different titles and prices i have seen for 
the DTXpress, one supplier has called it 'DTXpress', one 'DTExpress' 
and also 'DTXpress 2' and 'DTXpress 2k'.  I am thinking about buying 
a set and I am wondering the difference...

Also which kit has the 'new 3 zone snare drum pad'?  And how much 
would I expect to pay for one of these kits?

Any help would be greatly appreciated.