When my keyboard signal is sent to an amplifier, and the output is going to be mono, when is it best to mix the channels? I have the Roland BK-9 which outputs stereo when plugging into both sockets, and mono if plugged into just the left channel (standard setup). Should I send mono to the powered speaker or main amp, that is mixing the channels at the keyboard. Or, should I send both channels and let the mixing happen at the mixer or powered speaker. Is there a right and wrong way?