Yamaha DTXpress/DTXplorer/DTXtreme

Hi,
Great group I have learnt an enormous amount reading through all the 
postings. But one thing I cannot work out is whether I should grab a 
second hand DTX kit or a new dtxpress kit. Prices are roughly the 
same, but I am assuming as the dtx is 18 months or so old that the 
progresion in technology to the new dtxpress could be a better 
option. Any opinions would be greatly appreciated.
Cheers from downunder.
Alan