5.1, 6.1 Or 7.1?
It’s all about realism.
1.0 Monaural Sound Systems
To understand the difference between 5.1, 6.1, and 7.1 it is helpful to know some of the history of sound reproduction equipment. In the beginning, all sound equipment was monaural(1.0). This means that all sounds came through a single channel and out of only one speaker. Unfortunately the sound quality was not very good.
2.0 Channel Stereo Systems
The first significant improvement to revolutionize the sound industry was the invention of stereo where the sound is transmitted using two independent channels. For any given number of audio channels, there is an optimal physical setup for the speakers that produces the best effects. (This is shown in the blue boxes embedded on this page.)
The was a totally outstanding improvement. For the first time ever, you could experience sounds traveling from one side of you to the other! A stereo system (2.0) consists of two-channels of sound produced by two independent speakers — left and right. This was the first time that listener felt a sense of realism for what they were listening to. People listening to concert music could close their eyes and imagine they were sitting in the middle of the concert hall. Any equipment that did not have a set of speakers rapidly became expendable.
5.1 Channel Systems
5.1 Channel A/V receivers have five full frequency range channels. These channels are left/right, center and left/right surround channels. For best results, we recommend that you follow our speaker placement guidelines when setting up your home theater.
An additional subwoofer channel (the .1 or LFE channel, Low Frequency Effects) adds very low frequency sounds for music sources and special effects on movies from DVDs.
6.1 Channel Home Theater Systems
6.1 channel systems have an additional rear-center channel speaker for a total of three front and three rear speakers. 
6.1 channel sound provides more precise positioning of sound effects and creates a more enveloping soundfield.
7.1 Channel Home Theater Systems
7.1 channel receivers have three front channels, two surround channels, two surround-back channels, and a subwoofer channel. The recommended speaker set up or a 7.1 channel sound system.
