I’m still working with Adobe Tech support on this, but here’s a little more information and a workaround that might help.
First off, I updated the video drivers which didn’t address the problem.
However, I found that if you select “external device audio” instead of “desktop audio” in the Program Monitor Playback Settings dialog box, video will play correctly on the desktop AND the external device. (Of course it also disables audio playback from your computer – so it’s not a perfect fix.)
Hope this helps.