Yamaha DTXpress/DTXplorer/DTXtreme

Can someone explain the difference between a dual zone snare and a 
stereo snare for me?

I found a used dtxpress (older model) with the single zone snare 
that I am going to buy.

I wanted to upgrade it to dual zone so I can get the rimshot, but 
saw on the message board that it is going to take 2 inputs on the 
brain.

How is is possible that the stereo snare on the new dtxpress only 
takes one, but if I get a different aftermarket dnare it will take 2?

Is it possible to use only 1 like the yamaha pad?  I am thinking of 
a Pintech ConcertTone.

Thanks

JJ