Yamaha DTXpress/DTXplorer/DTXtreme

Hello everybody,


Could somebody please tell me how expandable the DTXpress is? That is 
after the basic 5 piece kit (hi-hat, base drum, 3 toms and 2 
cymbals), how many more drums (sounds) would i be able to add to the 
kit? providing I buying extra pads and triggers of course. And is it 
possible to increase the DTXpress' expandibility by buying some sort 
of hardware? (i.e. to upgrade the module) If this were possible does 
it effect the quality of the inputs?

Thanks guys
pete