Yamaha DTXpress/DTXplorer/DTXtreme

Hi, Can anyone explain exactly what the limitations are of the DIY 
DTXpander. I have looked at the circuit diagram on this forum and I 
beleive that I can make one but I am not sure what the limitations 
are? I am right in thinking that I will be able to connect two pads to 
the one input and assign two seperate voices? Thanks, any information 
is much appreciated.