ARC REF6 and B@W DB2

Hello everyone! I have tried to connect an active subwoofer to my preamp ARC REF6. Right now I am using my REF 6 and Luxman 509, but already ordered ARC GS150. and my question is how i can connect that sub to my preamp.
The REF6 has 3 outputs (one of them for records and two regular) . When i have try to use one outputs for signal to my amplifier and other of outputs to connect RCA cable to sub i have loud click when i change volume from 0 to 1. the same click if i use mute/unmute (after the loud click sub is working). if the amp Luxman  is on, after a loud click they go to protection mode and need power off/on. Is it possible to use a sub with this preamp? thank all for help