how to hook up Subwoofer to 2channel stereo system

How can you hook up the Subwoofer to 2 channel stereo? I want to get more bass for my second system. I am using Pass X1 and X250 for amp and preamp. Speaker is Von Schweikert VR4 JR. I plan to get the Von Schweikert VRS/1 subwoofer. Please let me known how to hook up them, thanks a lot
Hook them up to your second pre out of the preamp. I am using Martin Logan Descent subs as a left and a right coming out of my pre amp. They blend in very nicely.