I have Comcast HD Cable, I have my cable box wired directly into my receiver with a fiber optic cable. I also have an Onkyo HT-R550 7.1 receiver hooked up as 7.1. When listening to cds, dvds, radio, and any other aux equipment it works properly and sounds great. But my question is this when watching HD cable and my sound set to PLIIx Movie some shows, programs and channels also work properly but others only out put sound from the LCR, LR, RR, and sub. And absolutely nothing comes out of LS, and RS speakers. This even happens on HD material that says its DD5.1. I understand how PLIIx Movie works thats why i dont understand how it is possible that the rears will play sound but the sides wont. now if i switch the receiver to Dolby Digital it works correctly and if i switch it to All Channel Stereo it plays out all the speakers. So is the problem with the way comcast is getting the signal to me? Standard def channels all work properly with PLIIx Movie.