Originally Posted by KennyPa
True but do I gain anything by having a 7.1 setup. If my receiver can't decode bluray audio tracks correctly.
Sure. With a well placed 5.1-speaker layout, there will be surround information that images closer to your left or right side and other sounds that will phantom image in between (appear to come from behind you). But this only works when you are sitting in the sweet spot. If you're not sitting exactly between your two surround speakers, then those sounds will collapse to the surround speaker closest to you, which is normal for phantom images.
However, if you extract the sounds that were going to phantom image behind you, and send those sounds to the speakers behind you, then their imaging becomes much more stable. You can be sitting anywhere on your couch and those sounds will always appear to come from behind you. No magic involved, just a pair of speakers placed behind you (makes it difficult for those sounds to appear from any other direction).
This is why some people prefer to listen to 2-channel music using 3 speakers: by extracting a centre output and sending that info to your centre speaker, those sounds (like vocals) always appear to come from their intended direction (middle of the soundstage) no matter where you're sitting. Same benefit for playing back 2 surround channels over 4 surround speakers: sounds at the left/right ends of the surround field stay at those locations and sounds inbetween/behind stay at that location, no matter where you're sitting. Same directionality, just greater imaging stability.
Originally Posted by KennyPa
Is Dolby Ex a 7.1 format?
No, Surround EX is 6.1 matrix surround format. The 2 surround channels contain some mono information that is exactly the same in both channels. With a 5.1-speaker layout, that mono information will phantom image behind you (with all the instability that phantom images have for off-axis listeners). If you have a 7.1 layout and apply EX decoding, then that mono information is extracted and sent to an additional pair of surround speakers behind you. Stereo information that was in the surround channels stays at the speakers along your sides.
So, 2 surround channels are decoded to 3 surround channels (left, right, back). You still get rear-vs-side imaging in the surround field, but the 2 rear speakers are run in dual-mono (since they're getting the same information).
If you have a 7.1-speaker layout, you're better off using Dolby Pro Logic IIx. The two rear speakers will each get an independent signal, allowing them to run as stereo instead of dual-mono. If you are listening to an EX encoded soundtrack, sounds that were supposed to come from both rear speakers will still be played back that way (dual-mono). But otherwise, you will hear sounds moving between those 2 rear speakers, as you would with any stereo pair.