Please let us know how you get on with the test. One other step you can try is reverting to Catalyst 15.11.1 Beta to see if that resolves the issue.
If it does not, please read this before responding.
I did furmark yesterday for 1h without any trouble.
I noticed something, when my computer freeze or the driver crash, the sound is alway passing by the HDMI cable between my graphic cards and my monitor.
I don't recall crashing when playing with my headset or when the sound is mutted.
I'll try playing with my headset only to see if I can confirm this.