I really need some help on this one. I was recently asked by someone to take a look at their home theater setup and see what I'd suggest they'd do to spruce it up. Given that their receiver was pretty old (only had Pro Logic), I suggested they get a new one and a new HDTV.

Well, I thought I'd done enough work figuring out their current setup, but I clearly did not. Otherwise I might have asked "where the hell is the signal from the subwoofer coming from?

Here's the setup: they have the usual 5.1 arrangement, with the sub being an in-wall model. I've identified every single wire coming back to the built-in cabinet the equipment is kept in, and there isn't a single cable for the sub. The old receiver just had a pre-out anyway, and there certainly wasn't a spare RCA cable in there.

So my next step was to take the speaker out of the wall and see what was what. I did so, and near as I can figure, the sub is wired in-line with the rear speakers. Is this common? If so, how on earth do you set up the receiver to account for that? I can't even tell how they did that on the old receiver.

I really need some help on this one. Thanks...