What is the difference between 2 Channel and 5.1 Surround Sound?

Stereo is two channels (Left + Right). 2.1 is stereo with a subwoofer added to the mix (Common on Hi-Fi's).

5.1 adds a centre speaker and two rear speakers. The two rear speakers add extra sound detail in movies and the centre speaker is used for speech.

For movies a decent 5.1 system will give a real immersive sound (as the person above said), for Hi-Fi though, there are some 5.1 mixes out there, but I've never heard them so I cannot comment on how that sounds. If you only have a stero connection going from your DVD player you won't be missing out on anything, all the sound is there. With a 5.1 system the sound is simply split with extra detail going to the rear speakers. 5.1 surround sound uses 5 separate speakers and a woofer to create an immersive audio experience. Because there are 5 speakers, sound can be better manipulated to give the perception of depth and distance.

2 channel sound, otherwise known as stereo uses 2 speakers to create the perception of depth. Obviously, this has severe limitations as to the realism of the experience. 5.1 is normal stereo with surround sound, a center speaker and a base box. you can also get 7.1 2 channel is just a basic left & right. 5.1 has left front, right front, left rear, right rear plus a fifth speaker (usually positioned centre front) for speech and then the big sub-woofer (which can be positioned almost anywhere) for the non-directional low frequency sounds. 2 Channel (stereo) contains 2 discrete (separate) channels of sound.