Many thanks to the persons taking the time to provide this resolution over a year ago.
I recently replaced two STB's as an upgrade to continue receiving certain channels. The new STB connected to a big screen Vizio box was losing sound when flipping between channels too quickly or jumping between two distant channels. After swapping out the box a couple times, replacing all the cables, and speaking with VZ many times, I found this posting. When I again called VZ about it, they were not familiar with this solutioin. After much consultation, they helped me get to the white screen menu, and the change was made quickly and has worked perfectly.
I had some difficulty getting to this new menu screen. The process that worked on my new model 7232 STB was:
with TV and STB on:
press STB power button, then press OK on the STB, then press Menu on the Remote.
The white screen of options comes up, and the audio line was changed from AUTO to L-PCM.
I powered off and back on, and the sound keeps working no matter how I change channels.