Has been around for a while now and is probably the most popular format for digital surround sound. 5.1-channel Dolby Digital provides a bitstream of digital data of up to six channels supplying the front left and right, center, surround left and right, and a subwoofer.
Just like Dolby Digital, DTS also provides 5.1 channels of digital audio but with less compression, this gives a slightly more accurate sound reproduction. Most home theater receivers include decoding for Dolby Digital and DTS.
Is a slight improvement on DTS, it basically provides an extra channel (6.1). This extra channel is a discrete, full-bandwidth back surround channel that can be played through one or two extra speakers. Presently only a few DVDs are encoded with 6.1-channel DTS-ES sound.
DTS NEO 6
An even newer development from DTS, allowing lower quality recordings in matrixed stereo (such as analogue TV broadcasts or VHS video recordings) to be generated into five or six full-bandwidth channels of sound for 5.1 and 6.1 systems.
Dolby® Pro Logic®
An older form of four channel home theater surround this consists of front left and front right, center and surround channels matrixed from the regular left and right channels.
Dolby Pro Logic II
Is a 5.1 channel system that takes a stereo or Dolby Pro Logic soundtrack and converts it to 5.1 playback. Benefits will include a greater surround sound experience and deeper bass.
Is designed to give surround sound improved directionality. THX EX provides a more fully 360° wraparound experience by adding another one or two "back surround" speakers to the speakers already present in a 5.1-channel system. The added channels share a matrixed channel of sound composed of information from the regular surround channels.