The instructions (hopefully the link works) have a diagram with this indicated:
"High Level connections should be made to the same binding posts as the main
speakers
Connect as shown above. Connect RED to right monoblock speaker positive (red) terminal,
connect YELLOW to left monoblock speaker positive (red) terminal. The BLACK should be
connected to ground at the pre amplifier. If the pre amplifier does not have a dedicated
ground terminal, then use one of the chassis screws at the rear of the pre amplifier.
NOTE:- MAKE SURE THAT ANY CHASSIS SCREW WHICH IS USED IS NOT CAPTURED
ON THE INSIDE WITH A NUT, THE NUT COULD DROP INSIDE THE UNIT."