Graeme, it isn't necessary for the receiver to be able to decode the new audio formats present in Blu-ray discs if the player can decode them. Your player can do this for at least Dolby True HD(I haven't checked the DTS capability)and send the PCM out via the HDMI output. So, your 661 allows for the realization of any audible benefit that may exist in this format on a particular disc.

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Enjoy the music, not the equipment.