I recently connected my Sky+ receiver to the Sony HT-SF1100 amp via optical. I notice that with some channels, however, the 2 rear speakers do not output coherent sounds..rather muffled broken incoherent sounds. This happened , for example, when I recorded the recent Liverpool v Everton FA cup game from Setanta. However when I play Bubble hits...I am getting 5.1 sound from all speakers. Is it a case that, with some channels, you just can't get 5.1? By the way I have the "Optical Output" in the Sound Menu set to "Dolby D" instead of "Normal". Thank you.