Hi Tim,
I had a look at this issue too, it seems that this is coming from network security feature most likely set up by your system administrator. When I accessed your site, I could not listen to the audio clips either. The requests to those files were forbidden with the following message:
HTTP/1.1 407 Proxy Authentication Required
I am guessing that the request is allowed providing that my proxy details have been set as you'd expect them, which is not something the app has control over. Another thing I noticed is that the URL to your files are pointing to a draft area "draftfile.php". That does not seem right, draft files are temporary and should not be used to serve content. Technically you might be able to access them if you were the user uploading them, but drafts are usually deleted with 4 days. The URL pointing to your resource should contain "pluginfile.php" in order to work both in a browser, and in the app.
That problem can often arise when copying content from one place to another.
I hope this helps.
Cheers,
Fred