There are a lot of people having the exact opposite problem I am having. With the newer nVidia drivers people are complaining that their TV no longer plays audio over the RCA jacks:
Here's how it works. The audio data is embedded in the HDMI video stream, multiplexed with the video data. If the audio data is present, the TV will play that audio signal and disable the RCA inputs. If there is no audio data present, the TV falls back to the RCA inputs. There is no setting to tell the TV to listen to HDMI audio or RCA audio. If the HDMI audio data is present it will be used.
It also appears that by default the SiI 1390 chip embeds an HDMI audio signal (because my TV ignores audio from the RCA jacks during boot up). So all I need to do is figure out how to prevent the nVidia driver from disabling the embedded HDMI audio, or override the setting and re-enable HDMI audio after the nVidia driver loads.
It's strange the many people are having the opposite problem and are able to work around it by messing with the EDID. Makes me think there has got to be a solution.