Hi Ronald,
Actually you can access these various "kits", but it's not so intuitive at present (we're working to make things more so).
If you are using your Yamaha keyboard as the MIDI playback device, you'll want to check in your User Manual for the keyboard to see which Instrument Patch number to use for each kit.
What that means: you will always use Channel 10 to access drum sounds (that's the MIDI standard). When you open a song file in Musician or Composer, click on the Drum staff's Staff Control button. You will see that it is set for Channel 10, and typically the Instrument Patch in the grid will be selected as "1 Acoustic Grand Piano". For most MIDI devices (eg. your Yamaha keyboard), this translates as "1 Standard Kit". Most (not all) also use "33 Jazz Kit" which on the GM grid is "33 Acoustic Bass". You'll have to check in your Yamaha's User Manual to see what other kits are available, and what patch numbers you should use for them.
Please note that the MIDI instrument patches can be numbered 0-127 or 1-128 - our products use 1-128; if your device uses 0-127, just add "1" to it for the corresponding correct number in our grid.
Enjoy
Sherry