Originally Posted by Franin
So the height channels are a copy of the surround/ rear channels?
Copy isn't the right word - it's not a bit for bit identical copy in the Height channels. The Height information isn't in the original content so it has to be 'derived' or 'created'.
PLIIz derives the Height information from the content in the surround channels. DSX derives (and some say creates) the height information from the content in the main L&R channels.
Neo:X derives Wide information from the front left/left surround and front right/right surround but I am not sure how it derives its Height information.
There are others in this thread who have vastly more knowledge of this than I do, but my simplified explanation of DSX/PLIIz above is correct to the best of my knowledge. Because DSX gets the info from the front R&L channels, I personally find it creates a much too front-centric effect and diminishes the all-important (to me) 'surround sound bubble'. PLIIz, getting the height info from the surround channels doesn't seem to cause this issue for me and preserves the bubble while also giving a nice ambient effect up in the Height speakers. It's not all that noticeable usually, unless you turn it off (which I can do simply by killing the amp that powers the Height speakers) and then you really notice its absence IYKWIM.
I have experimented with Neo:X for my Height channels but it does something odd which I dislike. Can't put my finger on it. If you have some 7.1 encoded discs, try swapping between PLIIz and Neo:X and tell me what you hear in the surrounds. Very noticeable on 7.1 encodes with a lot of surround activity - eg Transformers DOTM.
All of this is very subjective so everyone's mileage will vary.