Philb7777, I had the same question as you when I was going to hook up my REL T5 to my ARC D70Mk2. I'm not sure if your amps use the 4ohm tap as a ground, BUT assuming that they do...this is what I was told at ARC to do..
Hook up the red cable to the 8ohm right side, the yellow cable to the 8ohm left side and the black cable to either 4ohm tap.
This worked on my amp well. Not sure IF this will work on your mono amps, but should.. you could ask ARC as they will be very helpful and set you on the right track.
Hook up the red cable to the 8ohm right side, the yellow cable to the 8ohm left side and the black cable to either 4ohm tap.
This worked on my amp well. Not sure IF this will work on your mono amps, but should.. you could ask ARC as they will be very helpful and set you on the right track.