TIP do not run speaker cables close to AC cords. Keep away from each other as best as possible

The impedance issue makes sense. At this point I give in, I have spent enough time on this.

I (and the facilities I serve) am delighted with the sound using the single 1/4 inch cable. My only other known application at this stage is for my iPhone connected to the Bose (if my keyboard fails), and that has no hum; as well as the mic which sounds great using a SM58.

What I do not understand is how others with Korg Pa900 DO NOT have the problem...

Graham, I don't know of anyone that plugs into the RCA plugs from the output of their arranger keyboards or synths. Most everyone that uses that input is using it for line output items, which is lower impedance at 1.5-vots DC.

I searched everywhere in the Internet and called Korg's customer service, but they said they didn't have an answer and would call me back. That was three hours ago. Nothing yet. I suspect this is the case, though.

Back to sippin' Margarettas.

Good luck,

Gary