I've noticed a weird quirk with the TV. If I put a HD video file with surround sound support in a USB and play it back on my TV with it connected to my home theatre, the receiver says PCM and plays back only via 2 channels no matter what. The TV does say 'DTS surround' when I play the file, but it's PCM stereo on the receiver.
However when I connect the USB to my HTPC connected via the same optical cable and play it back on Windows Media player, it plays back in proper DTS surround. Any clue?