I just got a new soundbar for my tv, and I'm having trouble getting it set up since the Roku is using the HDMI port on the tv.
The soundbar has an HDMI out and an optical out, and that is all. The TV has 3 HDMI ins (none are ARC though), a 3.5mm aux port, and a lot of RCA ports (I think that is what they are called, the cable that splits into two or three with a red/yellow/white end). The TV also doesn't have bluetooth or wifi. And the Roku is the Roku Streaming Stick+.
Then you have your answer, you do not have the proper inputs and outputs for what you want to use. Time to upgrade or live without. Replace the roku stick and separate sound bar with Roku streambar that is both a roku and soundbar in one.