Yamaha DTXpress/DTXplorer/DTXtreme

I'm confused to the difference between the mono trigger pads,
and the stereo pads / dual zone pads?
Can the dual zone work in dual zone with other drum modules from 
other manufacturers?
i'm confused about the DTXpress module, it
has 1-8 inputs that are mono, but can use stereo inputs?
and the 9-10 are stereo?
I'm so confused how all this works with other modules.
Cause I want to be able to get a better module one day.
And want to be able to re-use my pads.

Thanks for your help,
Mike