A CD that is Multichannel

Jeffreybehr...It's more than that. A quick check of track 1 of this CD, (Overture) using my Behringer DEQ2496 analysers shows rear channels within a few dB of the front left and right, and a center channel signal that is about 6 dB down from the fronts (still quite a strong signal).

El, are you using some sort of signal processing? CDs really have just TWO channels. Maybe your processor is making more than what's there?
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Jeffreybehr...Yes, my processor is taking the digital data stream from the CD and applying Dolby PL2 processing. That's how Dolby works. I can do this with any disc. But the result with this particular disk is far and away more effective, and the "Dolby Surround" logo indicates that some deliberate effort was made in this direction when the disc was created.

I admit to being a bit puzzled. I could take issue with your statement that "CDs really have just TWO channels"...actually they have one digital data stream, and some kind of processing is always needed to make music out of it. This is unlike, for example, a mag tape recording where there really are two distinct tracks of information.

The bottom line is that whatever they did to this disc is a good idea.

I think that Jeffreybehr and Eldartford are both correct. It is my uderstanding that Dolby Surround was one of the first implementations of multichannel. The front left and right stereo channels exist of course, and then the diffeerence between the left and right front signal is sent to the rear as a mono signal for a surround effect. So Jefferybehr is correct in describing Dolby Surround as a matrix of only two channels. Eldartford is correct in saying that something else exists other than the two front channels as a separate data stream, i.e. the mono matrixed rear channel(s).

Markphd...Monitoring my DEQ2496 it is evident that the two rear channels are not the same. Their levels are different, and not always the same way as would be the case for a simple gain discrepancy.

Whatever, it works.