On toms and snare dual zone means head and rim shot. On cymbals it means bow and edge. But the nitro does not support either. If you want to expand, you'll need a better module.
For example the Surge module supports dual zone toms and snare, plus crash chokes. But not dual zone cymbals. If you want a kit that supports about about anything, get a ddrum DDTi interface and use a PC with A2D or other VST. But then you need a dedicated PC all the time. As you move up the $$$ line each module introduces more features. Also be aware that with each Alesis module you will need a new snake.