Hi,

MAIN OUT and SUB OUT provide the same output from the keyboard. That is to say they are at LINE OUT signal levels. MAIN OUT cannot be switched (does not offer user selections), but SUB OUT does. I would use SUB OUT if you want mono outputs. Go to PROGRAM MENUS/SEPARATE OUT SETTING to set the output to STEREO or MONO X 2. Look at pages 161 and 200 in the manual.

Maybe I have misunderstood your question and am offering a wrong answer. If so, I'm sorry. HOwever, I hope this answer helps you.

Chuck