If you're just trying to get the Roku playing through the receiver, then the simple way is to connect the Roku to the AVR (Sony). (The limitation of this method is that it works for Roku, Blu-Ray, satellite box, cable box etc. but will not help if you want to listen to over-the-air TV coming through the TV's built-in tuner. That's important to some people - others have forgotten that that exists.)
If you don't want to do that, then you need a path for sound from the TV to the AVR. This breaks down into a couple of basic options: Using HDMI ARC (if supported by the TV) or running some additional cable such as an optical cable. I suspect that if your TV supported ARC, you would have noticed that one of the ports says "ARC". However, 9 years old sounds like its "new enough" that ARC was already around by then, so possibly you missed it. Possibly it's the port that the Roku was already plugged into so you didn't look closely at it.
