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

Post removed 

sorry, i'm beginner, unfortunately i can't understand what is mean common ground. thank you for you help.

What Curtis is saying is to find a sub that hooks up High Level

or Speaker level

 dumping down the Tube preamp output impedance with a sub is a fool's errand and affects your great midrange

Many good subs can go speaker-level high out l Rel Vandersteens etc.

 the DB1 is at its best with a surround sound processer in a home theatre

   Cheers JohnnyR Audio Connection

Jensen Transformers SP-2SX Stereo Speaker to Line Audio Converter/Isolator

Now SUB is working!!!!!!