[bob]

Bret Ludwig wrote:

But what about four, five, six, seven, eight, or more channels? Where
is the evidence for their benefit?

The typical goal of home audio reproduction is to transport the
listener to the performance space. But just as a thought experiment,
imagine a different goal: to create the sound of musicians performing
in your listening room. How would you do that? By arraying speakers
across the front (ideally, one per instrument). Then the reflected
sounds would closely match those you would experience if there were
musicians instead of speakers.

(Obviously, this only works if you have a large room and you're
listening to chamber music. A symphony orchestra would sound terrible
in your living room even if it could fit.)

Now, let's go back to the main goal--transporting you to the concert
hall. What stands in the way of that? Most obviously, all those
reflections that your brain will inevitably interpret as, "I am
listening to this in my living room." The way around that is to
provide extra information coming at you from different directions, and
that takes extra speakers.

This is just theory, of course. But it's important to remember that
5.1 and larger systems didn't evolve by accident. There was plenty of
research into configurations that improved reproduction of sound space.
(Maybe Mark Ovchain will come back someday and remind us of his work in
this field.) I'm sure if you search AES for articles on multichannel
reproduction you'll find loads of relevant material.

bob