I got a new 4K Vizio VIZIO M55-E0 55" Display along with the LG UP970 4K Blu-ray player for the holidays. I hoked up one HDMI cable to the TV for video and a second audio only out to an older Sony 5.1 1000W home theater system receiver. Everything was working great when I went to watch Cars 3 on 4K Blu-ray last night, but about half way through the movie I went to pause it once I realized that I had forgotten to turn HDR deep color on. Once I did that, I went back to the movie and no more surround sound. I even tried turning HDR back off again, but still no surround sound. Now it doesn't matter if I try to play DVDs, standard Blu-rays or 4K discs, I'll get a perfectly working picture and two to three seconds of quick surround sound at the beginning of the movie, then complete silence from then on out. I understand that since the second HDMI port is passing audio out only to the receiver and not video, that it doesn't matter that the receiver isn't 4K or HDCP 2.2 compliant, so what could be causing me to lose surround sound here? I previously had the surround sound system hooked up to a traditional Sony 1080P Blu-ray player for the last several years, and they always played just fine without these new issues that I've been experiencing. I would hate to have to rely solely on the much inferior built in TV speakers for audio, as I'm not going to be able to afford a new surround sound receiver or speakers for the foreseeable future.