...this is a problem with your HD set top box. Either ask TW about firmware/software udpates, or swap it out for a new one. While I'm not 100% certain in your case, such audio nonsense requiring multiple box swaps is way too common IME.
I have been having trouble with my digital audio signal constantly switching between the HD signal (5.1) and the 2 channel sound. On some channels the receiver switches quite frequently (several time per show)leaving a 2-5 second loss of sound as it reconfigures.
The setup I have now is:
High Def Cable Box from Time Warner hooked into Sony Receiver
Sony TV hooked into Sony receiver
Sound comes through speakers hooked into receiver
All connections are through HDMI
Is this a cable box problem? a compatibility problem? receiver? hdmi?
Thank you for any help you may be able to provide as I am at a loss on this one.