I only started having this problem when my 8300 HDC was updated to the Navigator software. A temporary, although undesirable, solution was for me to use a component cable for the video connection to the TV. At least now the audio output setting remains on Dolby Digital without resetting to PCM stereo (HDMI). I intend to call TW support to see if they have a fix or a patch they can send to my box to resolve this. Failing that, I understand that the newer Cisco 8640's may not have this problem, and I can try to swap out the box.
My SA 8300 HDC STB is connected to my Panasonic plasma via HDMI for video only. I use an optical digital cable connected from the STB to my 5.1 home theater receiver for the audio. I have set the audio output in the Audio Settings on the STB to Dolby Digital. Everything works fine until I power cycle the 3 components. I find that, when powered back up, the STB will automatically switch from Dolby Digital output to HDMI PCM stereo audio on its own. This switch also occurs if I power cycle only the TV by itself. I did not have this problem prior to the Navigator update this week. I see several posts on other forums regarding this issue, and was wondering if anyone on this board had the same problem.