The latest Channels for iOS beta now supports an audio only mode. When watching a channel or show, use the context menu (More button or Tap and Hold item) to choose Audio Only.
This will play back the content with only audio. This requires transcoding on your server, but it's light since it's discarding the video track and only transcoding the audio to AAC.
This is useful for things like car trips when you want to save on data, etc.
Let us know if you run into anything funny.