I go from my Roku Ultra directly to my Vizio P75-C1 via HDMI. The audio comes back to my Denon X2300W via ARC. I get Dolby Digital+ 5.1 sound that way. With ARC turned off I also have the Vizio send the Denon audio via optical cable. That way the Denon is receiving Dolby Digital 5.1 but not plus. I just tested that, both ways, using HBO-Go from the Roku. The audio was good both ways but via ARC was better.I only get 2:1 on HBO GO from optical out on Roku Ultra.