about your question "Does it work in other mobile browsers on the device, or only from a PC"
no, there are browsers on PC. I have just Avalanche browser on Intermec CN70e
If the CN70e is WM6.5 based then you should be able to use the built in Internet Explorer browser for testing. If it is Android based, there is surely a browser built in that you can try to use. I would confirm whether or not you can play the audio in the native OS browser before troubleshooting why its not working in the Wavelink Browser.
In native web browser (Internet Explorer) sounds are also not working..
This is the same screen from built in IE browser and here UI layout is correct: