Are you sure your TV outputs a 5.1 signal thru HDMI? If it isn't or if the program you are watching doesn't have DD encoding you won't get much/anything out of your rear speakers. "standard decoding" as well Yamaha's DSP modes sometimes can simulate a false surround field with non Dolby...
Does your Denon have Pure Direct on it and is the light lite up for it on front of your receiver? It should be a bright blue light. If so turn it off and see if your video doesn't come back.
Watched it last night and It looked wonderful. Audio wise it was really good but palled in fullness compared to the old laserdisc. As a most titles do. I.E. Twister