No solution that I've found. I ended up buying a ATSC Converter Box (TV tuner) and a splitter for my coaxial cable so I could run it to both my Roku TV and the Converter Box. I use the converter box to watch CBS and Roku's Live TV channel to watch everything else. Annoying? Definitely. But much cheaper than buying a new TV.
Also this proves conclusively that the sound problem is indeed with Roku's Live TV channel. After all, I can watch CBS from the same TV with no audio issues by using the TV tuner box.
Though I'd much prefer it if Roku would admit there is a problem with their Live TV channel and then get to work on fixing that problem.