Adobe Captivate 8 HTML 5 Publish - no audio for some?

Here's the short story: I have an HTML 5 published Captivate 8 course that works in Chrome 44.0.2403.125 m, IE 11, locally on my machine, and through our Amazon S3 server. My colleagues in Geneva and France, however, see and hear the course on our test server(UST) but only see it on our Production server and don't hear it. Argh. These colleagues are using IE9. Chrome works fine for them. Has anyone identified a fix for this issue? Our client will need to distribute this widely so upgrading to IE11 or going to Chrome is not an option. How can they see it in our test environment but not the live environment?