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You would need to set up the blu-ray player to output the audio in bitstream instead of PCM. When audio is sent as PCM to your receiver from the blu-ray player, then the receiver can only display that it's PCM because it isn't decoding the signal and doesn't know what format it is. If the receiver is sent a bitstream and actually does the decoding (for Dolby TrueHD, as an example), then the receiver will be able to display that.