Yamaha DTXpress/DTXplorer/DTXtreme

okay...i found the answers to the computer connection question on the 
website...thanks guys...very helpful! But, i have a question regarding using 
the GM keyboard sounds...i'm trying to access the bass & guitar sounds but 
so far no luck. I've managed to pull up a piano sound and assign it to one 
pad, but now all i seem to be able to change is the note value of the key 
and not the sound itself. Am i missing something? And is anyone rewriting 
that manual???