As standard you do not get audio over the DVI port on R9 devices.
I got audio working correctly over DVI using an old DVI to HDMI converter that shipped with one of my previous ATI graphics cards, the HD4850x2.
They are still floating around on ebay, and look like this:
Just use a standard HDMI lead to your monitor or TV and you get full 5.1 surround sound :)
Have fun watching youtube in 5.1 :)
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