Hello, I am not a stereo buff and my knowledge is limited. I have been putting together a system for my very large backyard patio and yard. Right now its only Audio, Next year I was planning on getting a large screen TV. And have surround sound. So far I have : Denon AVR 3300 4- Klipsch 650-AW outdoor speakers My next purchase was going to be a outdoor Klipsch 800 sub woofer or two. and that is why I am here. On the back of the Denon AVR Receiver I have a place to plug in a powered sub, that leads me to the conclusion that if I get the Klipsch 800 passive sub woofer I will need a Amp also is that the case ?