It is a very simple circuit. Basically you run a wire off of each channels positive output and run it through one or two rear speakers (in series) and throw on a volume control. You need the rear channels placed as far back as you can to add some delay. Used it once 20 yrs ago for "home theater" off of my two channel system. I was quite surprised at how natural it sounded if you can set it up right. I would guess the added demand on the amp is minimal.
