OK, I see your point.
You can have some solutions but you I guess you can't really control everything under the master volume control, on the SD1... (I'll try that on my SD1 later...)

Another solution:
You can use "another" mixer only for your keyboard (connecting the output of "that" mixer to your main mixer). There are lots a mini mixers avaiable, and you can put it even on the keyboard.

Luis Santos