Jake, just following up a bit on Adrien's excellent explanation of surround processing, it should be kept in mind that in the concert hall the majority of sound reaches us as reflected ambience from the sides and back, rather than as direct sound from the front. Extracting this ambience which is present to varying degrees in all recordings, but is confined artificially to the number of channels available in the format, and then sending it to the surrounds where it belongs, increases the reality of home listening. We're not confined to the number of channels as were the producers of the recording; the Stereo Police won't bust us for using too many speakers.
