I'm not an engineer so I don't know the answer but, if Cable TV can handle the current level of video, isn't there enough capacity already for any or all audio demand out there?
Cable and TCP/IP share the same pipeline, they're both two-way (when you change channels or order a movie on-demand you're sending a signal back to the mother ship,) and from what I understand audio streams are 10 to 20 times smaller than video streams.
I'm not trying to be argumentative ... just curious. I used to hear the case you're making with respect to video, yet video streaming keeps expanding exponentially and you can't listen to a radio or TV show without being urged to go find more streaming content online. If bandwidth were a scarce resource I think we'd be pounded over the head to conserve!