Experiment proposal: Use CC-BY-SA for some recordings, and other licences for other recordings. A year later, measure how many copies of which recordings are available on internet. (I don't recommend it seriously, but I would actually like to see the results.)

Hypothetically, would it be too big problem for you to use different licenses for audios of different articles, based on how the article author feels about this topic? Yes, your competitors could legally take some of your audios, but not all of them... so their satisfied customers would then come to you for the rest. Depending on numbers, the gains could outweigh the losses.