I managed to solve the problem, though I'm not sure how. It turned out to be something wrong with the TV. Once I reset the TV to "factory settings", the audio came back. After the reset, the individual audio settings remained as I indicated in my original post, so I don't know what changed.

Everything worked just fine until yesterday afternoon, at which point I suddenly lost audio when using HDHomeRun app on Roku. I have tried every audio setting on the Roku and on the TV, but I cannot get the audio back. Audio works just fine on other Roku applications.

- HDHomeRun FLEX DUO ...

Thanks, but DIY is specifically what I'm trying to avoid. I have enough DIY projects to make my system look like a science project. I'm trying to remedy that.

I have a TV antenna mounted in my attic, connected directly to an HDHomeRun Flex. A single Ethernet cable enters the living space and connects to my router, so I can watch OTA TV anywhere in the house on a Roku.

I was thinking that it would sure be nice to be able to do the same with OTA FM radio ...