Hello Friend
You can set one of the assignable buttons to turn off and on whenever you want. I configured the assignable "F" button on my SX900 to do this.
Go to the functions of the assigned buttons -> Category: Overall ->
Function: Part On/off -> One Exit. Still in the function, go to Style (at the bottom of the display) -> Select what you want to turn off or on. Ready!
I selected channels 9, 10 and Audio Style (at the end) + MIDI drum channel 10. This button always turns off everything at once. But you can select it your way.
Good luck!
Enildo