My receiver doesn't have HDMI so I have to use optical but HDMI carries sound. In fact if I did have HDMI in my receiver I still would connect my 4k blu-ray directly into the tv because I want the shortest distance possible to it. I'm guessing some receivers boost the signal a little to compensate but I want the best possible picture and sound coming from my baby. My OPPO was 550 bucks and they aren't going to make them anymore. Bastages!