Connect your Blue-ray to the AV with HDMI - I assume that you have already connected your AV to TV with HDMI ?
According to Marantz website FAQ:
How to output HD audio with your Blu-Ray player
Why is my Blu-ray player not outputting high-resolution audio (like DTS-HD Master) bitstream? Please first make sure that an A / V receiver is connected via HDMI which can decode the respective audio format, The Blu-ray player will need to configured to output Bitstream audio via HDMI". Insert a Blu-ray HD disc that contains HD audio, and launch it ( You may need to ensure that you have selected the HD audio through the menu of the Blu-ray disc.While the film is running, press on the remote control the MODE button and select the option "BD Audio Mode". In order to output the HD sound formats, you must set the value of this "mix-audio" change to "HD Audio".