I didn't require a thing! Since I was using the speaker leads for my mains, I had the XO at 80 (I use 120 for the surrounds per THX). I guess I could have rerun Audyssey in this configuration, but it worked well enough for my curiosity. While you have speakers disconnected, listen to a favorite song or section of an action movie on the subs only! That is enlightening and redefines what it is people mean when they talk about subs being tight!