This isn't the best forum for this topic but as there isn't a forum dedicated to decoding and it is related to AV amps, I figured it was about the best place for it. Basically I'm trying to understand all of the various different surround sound decoding formats there are. This came about because of a quick and simple test I did with LOTR TTT trying to determine whether it sounded better in DD or DTS. I was surprised to hear that there are major differences between the 2 formats (on this disc). I played the very first scene (about 2 minutes in) with Gandalf on the bridge as he strikes his staff to break it. In DD EX 5.1 there is music and a lot of sound effects coming from the 2 rears. In DTS ES 6.1 the only sound to be heard is a small crack after his staff strikes the bridge and nothing else. I did a bit of further checking and from the start of the film as the camera sweeps across the snow covered mountains, there is music coming from the rears in DD but absolutely nothing in DTS. I then proceeded to check some other discs to see if it was a DTS issue or specific to this movie/disc. So I tried Gladiator and it worked fine for both DD and DTS. One thing I did notice however is the encoding is different between the 2 discs but only for DTS. The following formats are displayed in the window for each movie/format: Gladiator DD: DDigital EX TTT DD: DDigital EX Gladiator DTS: DTS+Neo:6 TTT DTS: DTS-ES Disc6.1 So although both discs have DD and DTS-ES on the sleeve, it is in fact a different flavour of DTS-ES for each disc. pez kindly pointed me in the direction of this site: http://www.hometheaterhifi.com/volume_11_1/feature-prologic-iix-3-2004.html which explains some of the formats but it doesn't explain what the difference is between DTS+Neo:6 and DTS-ES Disc6.1. So does anyone have the definitive guide to surround sound decoding which lists all of the various formats and flavours and which will help me in trying to understand which format is the best for each particular disc I own? Or should I just let the amp do it automatically and have the rears set to Auto or have the rears (7.1) always switched on?