Okay, I played with a few functions with an X360 controller plugged in, and here is what I found:
-BUTTONS-
dbJoystickFireA() = A button
dbJoystickFireB() = B button
dbJoystickFireC() = X button
dbJoystickFireD() = Y button
( The following use the
dbJoystickFireX( int button ) command )
4 = left bumper
5 = right bumper
6 = BACK button
7 = START button
8 = Left Joystick Pressed
9 = Right Joystick Pressed
...and Twist X & Y control the right joystick, giving a value of 0 to 65535, as opposed to the JoystickXY() which retrieves -1000 to 1000.
I have not found a way to vibrate the controller or use the triggers in DGDK, but the official X360 controller code is
available free, but it's not as easy to use.
Hope this helps someone!