hi ,
it s also possible to use an old Roland OCTAPAD ... i have it in version 1 , the one from 1983

, it is capable to send MIDI "program change" instead of regular midi notes ... this way you can switch between 8 kits on the fly ... I assume later models also can do this ...
But be carefull , switchin kits on the Drumit 5 is not instantaneous ... it takes a little time , much less than half a second , depending of the Dsounds size maybe ... that can cause the first kick stroke to be silent .
I dont know it this was improved on the D3 or D5mk2 .