If matrixing is so bad, they why are there movies encoded in 5.1 EX? They are meant to be that way, so there is obviously no harm in having some of the surround info sent to the surround back speakers. To each his own, but I've never heard anything odd or bad while using the PLIIx or DD EX decoders on my 7.1 system, I only get a greater surround field. The logarithms used by the decoders are very good, after all the decoders are made by dolby, and you are listening to a dolby digital track most of the time, so I don't see where there would be any problems or issues with sound coming from somewhere it shouldn't.
I wouldn't say using a PLIIx or EX/ES decoder is adding distortion since it's a DSP, it's not like you are using the Cinema DSP found in yamaha receivers, which do add reverb and other undesireable effects, those decoders just redirect some of the sounds to where they ought to be, but aren't. The only difference between PLIIx and the DD EX decoder is that the PLIIx decoder will create a stereo surround back whereas the DD EX decoder plays the same sounds from both rear speakers in a 7.1 setup.
The first 3 Star Wars movies are all encoded in 5.1 EX so if you want to hear them how the director intended them to be, then I guess you need to get a rear center channel and use something with a DD EX decoder, and since the flags don't work proplerly on those discs, you have to manually turn them on, which doesn't add anything artificial to the original DD track.
"Matrixing" is a troublesome word, in that it is used to describe two different processes. The kind of matrixing that is done with Dolby Pro Logic (and the center rear channel in Dolby Digital EX and the matrixed version of dts-ES) is where they take, in the studio, more channels than the finished product can contain, and mix them down in a special way to fit on those fewer channels. To make life simpler, let us confine our discussion for the moment to Dolby Pro Logic (hereafter referred to as DPL).
With DPL, they have 4 separate channels in the studio. The front right, front left, front center, and rear (also called "surround", which is why it is "S" in the quote below). These four channels are then mixed together down to two channels in a special way:
The L and R inputs go straight to the Lt and Rt outputs without modification. The C input is divided equally to Lt and Rt with a 3 dB level reduction (to maintain constant acoustic power in the mix). The S input is also divided equally between Lt and Rt, but it first undergoes three additional processing steps:
• Frequency bandlimiting from 100 Hz to 7 kHz.
• Encoding with a modified form of Dolby B-type noise reduction.
• Plus and minus 90-degree phase shifts are applied to create a 180 degree phase differential between the signal components feeding Lt and Rt.
From:
http://www.dolby.com/assets/pdf/tech_library/208_Dolby_Surround_Pro_Logic_Decoder.pdf
Your DPL decoder at home reverses this process to give you 4 channel sound from a two channel source. This whole scheme was developed for theaters to use, so that there would only need to be two channels of sound on the film. There was not room on the film to easily add more channels, and also, this way, they could use existing projectors with two channel readers, which then feed the signal to a special decoder. But it also is perfect for two channel VCRs and 2 channel sound on analog TV.
Now, of course, they can do sound differently than when DPL was invented, and they can keep the channels totally separate from each other. Dolby Digital and dts (in their 5.1 versions) do just that.
Basically, the matrixed Dolby Digital EX and the matrixed dts-ES mix the rear center channel in the right and left rear in a manner similar to how the front center channel is mixed into the front right and left in DPL.
Now, finally, we can get to the other idea of matrixed sound, and that is where you make up channels that never existed in the original recording studio. This is what happens, for example, when you apply DPL IIx to an ordinary two channel CD. The recording studio did not have a mix for 7.1 sound; they had a two channel mix. The processing that is done at home in this case moves sound that was intended for the front right and left speakers to other places. Hence, it re-directs, or mis-directs, the sound to other places. Now, whether this creation of previously non-existing channels is a good thing or a bad one is a matter of preference. But it simply is not what was originally mixed, whereas the result of using DPL on a DPL encoded movie soundtrack is not creating any new channels that did not previously exist, but is only recreating what was in the mixing studio before it was forced onto only two channels.
