How do i get my Yamaha DTXplorer drumset to work with Guitar Hero World Tour?

One of the diretors on guitar hero said quote "Guitar Hero director Brian Bright confirmed that Rock Band (the original one) instruments would not only work fine with Guitar Hero: World Tour, but that you could use any electronic drum set with the game as it will ship with a MIDI connection on the back of the drum kit."
I tried this but i can only get 3 pads to work. The blue one when i hit the first Tom. The Orange one when i hit the Crash, and the Yellow one when i hit the hi-hat. All others dont register to any other drum. Is it possible to fix this so that all of the drums work?