In this instance it would be disabling the ati stream feature.
I'm still curious to the actual cause of your problem because I couldn't reproduce it on my system with the same card. Never the less I'm glad the problem was solvable for you.
Backing up to disable the hdmi audio feature you woudl just want to go into control panel -> sound and disable the hdmi audio device in the window that appeared there. It should display as "Amd Hdmi output"
Disabling mine actually solved a problem I had with my microphone, perhaps it could help with your issue as well.