Hi Rikki
Does the Yamaha have a Midi voice bank, i.e.- the Midi voice contains no sound but just sends the appropriate commands (To select the voice) to the SD 2.
If it does then you can just edit it to send the correct information (Voice selection) to the SD 2.
It should then be easy to change the style sounds (A drum kit is just a sound that has different instruments on each key) to select the Midi voice.
Hope this helps

Bill