Yamaha DTXpress/DTXplorer/DTXtreme

Hi, I am reletively new to E drums and I am having a few headaches 
with adding extra pads ! Can further pads be added to inputs 3,4,5 by 
use of a stereo splitter? I have already used the 9/10 input via use 
of a stereo splitter for an extra crash but I would like to add a 
further two pads! Also can the HH65 hi hat controller be used as a 
foot switch to increment drum kit voices, via the extra KP 65 input 
whilst playing? Lastly, is the RS70 rack the same size as the RS75 
rack? Thanks very much !