I've noticed that you are getting some around the bend answers on the
theory of surround sound.  IT IS SO SIMPLE!!!
Heres how it works.....
First, at the time of filming or in the audio room, there are 4 microphone
tracks recorded separately.  Then the echos and sound effects are mixed
in, and then they are mixed into two tracks - for ordinary stereo.
But its in this encoding process that all the magic happens.  Its not all 
that complicated as the guys at Dolby would have you believe, when they
use the words Dolby-Encoder.  What actually happens is the left and right
channels are left completely alone.  The Center Channel is recorded in
Mono- thats with the same wave going to the left as the right.
This is easy to understand.  The decoder will then analyse the incoming
signals and pull out the mono track from the left and right signal -
sending the mono signal to another amplifier.  Thus in theory we have
just created a 3 field surround-sound effect.
The magic happens with the rear channel, and the way they get it into
the stereo signal.  Instead or recording the track in mono, they record
it in reverse mono, which is a mono signal, but fed out of phase to the
left and right channels. (Effectively one wave is going up, while the
other is coming down).
This is where a good decoder will come in handy, it takes a computer to
pull the out of phase information from the signal and then send it
to an amplifier.
There you go, HOW to encode Surround Sound!
Heres an experiment you can try if you have access to a surround sound 
amplifier and a portable walkman.
1) get a left-right to mono - RCA splitter.  (2 in 1 out)
2) Get a mono to 2*Mono splitter for RCA. (1 in 2 out.)
3) Get a RCA wire and split the wires, and reverse the two wires inside.
   making the ends reverse polarity.
4) Get a walkman.
plug the walkman into the stereo inputs with the the 2 splitter, so that
there will be a mono signal being fed into the stereo.  Turn on the surround
sound and only the center channel will have sound coming out.
Do the same as above, but plug the spliced RCA wire into one of the
left or right channels, just before the amplifier.  Turn on the
Surround Sound and the only sound you will get should be from the
rear speakers.
The guys in the Surround sound Labs use a glorified version of the above
with proper mixing, echos, bass & trebel and interference stoppers.
Don't try the above if your warranty is void.  It doesn't always work
on all models. 
                        Dave.
--- GEcho/32 1.20/Pro
---------------