Yamaha DTXpress/DTXplorer/DTXtreme

I got a DTXPRESS 2 for christmas... and I've got a little problem 
which is annoying me.  I set up my own drumkit, but now if i hit the 
first tom hard enough it makes a hi-hat sound.. and if i hit the 
second tom hard enough it makes the sound of the first tom.
can someone please tell me why it's doing this and how i can stop it?

Thanks