have you tried loading and manipulating audio using the hypeDocument.extensions?
Here’s more: Extend Tumult Hype with JavaScript: hypeDocument.extensions
We had trouble with audio and solved it using this method.
If you do attempt to implement this, place your extension in HeadHTML and make sure that, before it, you had the hypeDocument.getPrivateContainer function which you’ll also find on that page as it’s required by the first script I linked to.