Try removing the channel from the Roku home screen by navigating to the channel tile, pressing the * key on your remote and choosing 'Remove channel'. Then restart your device from Settings>System>System restart. Once your player starts up again, add the channel back once more.
I already tried all combinations, either setting audio to "Dolby Digital" in combination with "Auto DD" and "Stereo" as well as other audio options PCM, Dolby Digital +, etc. None of them work. HD Homerun for Roku is the ONLY channel without audio... I do not think we as users should worry about special configurations.... we should be fine selecting "auto" in both of them, and let SiliconDust guys to come up with a decent app that just works. So far, it doesn't (Feb 1st 2021)
Since my original post, I got the impression Roku was not going to spend time to support an older model like Roku 3. I since moved on and got a Fire Stick. Zero issue. I like to "tinker" and Fire Stick gives you more freedom for doing more.
I am using the new SteeamingStick+ and does not work... video is ok, but no audio... unless you are ok reading the closed caption text to figure out what is being said, I do not recommend this app/channel, it is not finished. All other apps/channels work just fine.
It looks like TVs and projectors without the ability to decode Dolby Digital or AC3 audio over HDMI aren't supported: "To hear audio, you need a TV, AV receiver, or soundbar that can decode Dolby Digital or AC3 audio over HDMI. Most modern TVs can do this, though we’ve noticed a few Samsung TVs cannot." https://info.hdhomerun.com/info/roku