Yamaha DTXpress/DTXplorer/DTXtreme

I know that the DTXtreme can connect more pads, and it has more pad 
sounds than the DTXpress. But apart from that, can anyone tell me 
what advantages it offers over the DTXpress?  (I note that there is 
much discussion of combining the DTXpress with Roland hardware and 
other brand products, but virtually no talk of upgrading to a 
DTXtreme.)