Would it not just require a plugin that mutes the wav when something comes through the line in? I think you'd be better off posting this in the Centrafuse section, as each frontend will require a different plugin. It may even be a feature already include, that you don;t know how to turn on

If it's not a feature, you could request it?
You could also just have a 3rd party app running in the background that does the same thing.