I just bought a refurbished 2013 Mac Pro from Apple to replace a 2009 Mac Mini, and I noticed that the sound level through HDMI is at least 40 dB WEAKER than when I use the digital optical-out cable. I am connecting to a Denon DN500-AV. I also notice that the Mac Pro is always piggybacking an audio signal on the HDMI, even when I go into System Preferences -> Sound -> Output and select Digital Out in place of HDMI. As a result, this is causing the receiver to attempt to use the (weak) HDMI audio and ignore the correct digital optical-out audio. Is there any way to force the Mac Pro to not do this piggy backing of audio onto HDMI? Thanks.