What you are doing (and it is fine to do it if you like it) is generating new channels that do not exist in the soundtrack itself. It is exactly like applying a DSP to a 2 channel recording and generating more channels. It is directing sound to a place where it wasn't in the recording studio where they mixed it. That is misdirecting the sound. But if you like it, by all means, do it. And 5.1 EX tracks have encoded in them surround back material, that is meant to be decoded by either an EX or PLIIx decoder. Now I know it's still not a discrete channel, but it is still inteded to be there even though it's only a 5.1 track. And as for stereo material being used with a PLIIx or EX decoder, I prefer to hear dialog out of the center speaker, so I use the decoder vs. using 7 channel stereo... but it's all a matter of preference.