L-R - R-L circuit for extra speakers

In the past I have wired a pair of extra speakers in series across the positive outputs of the terminals of a seperate amp to give the L-R/R-L signal to these speakers. I was wondering if anyone knows of a cicuit similar to the Carver/Sunfire "seven axis" feature where the side left speaker gets the L-R and the side right speaker gets the R-L program info.Thanks.
I did that bit for awhile (wiring extra speakers across the positive outputs of an amp in what is the so-called Haffler circuit) but I later bought a line-level passive surround sound processor called the PhaseAround. I bought this from John Sunnier (of Binaural Sound) who was liquidating the PhaseAround stock a few years back. It is/was an excellent unit; used it primarily for music. Unfortunately, its innards got zapped a couple of weeks ago during a thunderstorm and I spent a good deal of time on the internet looking for a good substitute. In the process I stumbled upon the U.S. patent for the PhaseAround circuit at http://www.bpmlegal.com/xsursnd.html. This page describes what the circuit does (extracts then outputs the left-minus-right and right-minus-left signals) and contains a drawing of the circuit. The drawing appears to be referenced to the patent itself for complete details. There probably is a way to obtain a copy of the patent, perhaps even over the internet. (I've notice in reading postings on Audio Asylum that some of the inmates have made copies of various patented circuits, etc. for their own use.
I solved my own problem by using an old Yamaha AV receiver for the surround output using its "concert" DSP mode. I suspect that the Yamaha DSP modes are basically left-minus-right and right-minus-left circuits. The sound of my new setup with the Yamaha driving my surround speakers is as good if not better than I got from the PhaseAround. I also have a Denon AV receiver which I use in my home theater setup, which has a "Matrix" surround setting that is great for music and is also probably a left-minus-right and right-minus-left circuit. Hope you find this info helpful.
Thanks Bill, now my hunt continues with some sort of direction. I will see if I can get my hands on that circuit drawing.Maybe someone else has another idea?
Doesn't the Chase Technologies processor embody the Hafler circuit as well??? A passive device that could be used several ways--speaker outputs into the Chase/ front & rear speaker level outputs or speaker outputs in/ front speaker out and RCA outs for a seperate amp(s) for rear and center.
I'll dig out the manual if I can find it; it was a fairly reasonable device ($100 or so) when available.
I've got a schematic for such a circuit in a blue book titled something like Experiments in Audio.

This site has rudimentary info on Hafler circuit.
Scanned a review of the Chase if interested:

Click on page you're interested in
Dooledog, thanks alot, your are a big help!