I have been having this CW issue also. I have one prime and one ceton infinitv usb that both exhibit this audio issue. Two different computers. I also still have one cable box, but that works just fine. Using the HDprimes quicktv also results in audio on this channel, indicating that it is a WMC specific issue. What I found was that if you call up the info while watching the channel, navigate over to the language section you will see English listed twice. If you switch to the other english, then audio starts working. The sub description for the non working selection is "content default" while the working audio is "music and effects". Problem seems to exist for my Hauppauge 2250 cards on the clearqam version of the channel, now that it is unencrypted again. Although the selection order seems to be reversed, i.e. on ceton and prime you switch from the second selection to the first, while on clearqam you go from first to second. It is still the music and effects that has good audio though.
I guess an OTA check would determine if the problem originates with the station or comcast, since it appears the audio is not where MC is looking for it to be. Unfortunately I have no antenna to hook up to test this myself.