Yes, that Denon has no HDMI inputs. So either he is using an HDMI audio extractor, which means he's only getting 2ch stereo for most of his services. Or he's got the HDMI going to a TV, then optical out from there back to the receiver. Which still could mean he's only getting 2ch stereo from his services on the Roku. And everything else if he's running everything thru the TV 1st.

Need to replace that Denon with a modern receiver. HDMI has made it so it is a necessary thing in any surround system these days.
Or you can get the new Roku Ultra, which has an optical output that actually works for 5.1 for that old Denon.

Sony DVD??? You know you can get a new Sony Bluray for less then $99 right.