Yamaha DTXpress/DTXplorer/DTXtreme

Ok, I just got this machine.  Love the sounds, its' groovy... But... 
when MIDI triggering it, I can't get the computer to trigger kick 
sounds.  It works with all the banks except k and K!  Why?!  I'm 
pulling my hair out because I suspect it's something simple but can't 
figure it out.  When I put other bank voices on pad 1 it works great, 
and when I put kick voices on ANY pad, I get nada.  AM I A MORON?  
(<rhetorical).  Please any suggestions. Thanks, Stu