This is a general HDMI debugging problem...
I have a collection of STBs (not sure of the chip set) that fail to send audio to certain repeaters or sinks. Instead silence PCM is transmitted. When connected to a particular Sony AVR, the STB sends the Dolby Digital audio just fine. When connected to an Onkyo, a Dolby Repeater, or a particular TV, the STB sends silence audio. I believe this to be a problem with some common middleware in the STBs.
My first thought was that it might be something with the EDID that the STB does not like, or is not able to parse. I modified the Dolby repeater to forward the entire EDID from the Sony AVR (the one that the STB works with) to see if it would then send the audio. This is not seem to work (although I still need to confirm it was indeed copied without being modified).
This does not seem to be an issue with the data itself, because if I connect the Dolby repeater after the working AVR, the AVR is able to passthrough the audio, and the Dolby repeater can decode it. So I believe the issue is more to do with the HDMI communication. I am not sure what other than the EDID would effect the STBs ability to send audio.
I would like to at least determine what it is about the Sony that cause good audio to come from the STB. Any suggestions in debugging this would be much appreciated.