What is the Power Amp Routing button for?
This button selects how the signal is routed to the amp. When the button is in the UP position, the mixer sends the signal from the main mix to both sides of the amp. When it is in the DOWN position the mixer sends the main mix to the left amp and the monitor mix to the right amp. This switch does not affect the line level Monitor Output and Mixer Output(s) on the front of the unit; these are always active.