It is a powered sub-woofer. I do have to plug in the sub to the wall to get power. But, I think you are right about needing an LOC. I called Magnolia Hi-Fi, where I bought the Denon Receiver, and at first they were saying to get the LOC, but then backed off, because they were thinking it would add distortion to the line. They told me to hook it up the "old fashioned way", which I did. That is, take the Front Left and Right hookups to the sub, and then from the sub, wire the Front and Left tower speakers, and tell the receiver that I do not have a sub. In this way, the full bandwith is transferred to the Front Left and Right. As it goes through the sub, the sub will handle the crossover (at 85 hz), and send the rest of the signal to the towers (Boston CR95 floor standing speakers).
It works, but It would have been nice to be able to let the receiver do the crossover work, rather than the sub. Oh, well. Maybe someday I'll spring for a new sub. My wife, on the other hand, doesn't like the "sub sound" at all!!! Even though I have it turned down, she still doesn't like that "low level feeling" that subs give you. I want to tell her "that's the feature, not the problem!" :)