I threw an R9 380 into my machine the other day, and with the AMDGPU drivers everything seems quite fine . . . except I no longer have any sound. I've tried setting the audio priority, but considering that sending test sounds to the device from system settings results in no sound either I'm assuming it's not a mere prioritization issue.
Opening up pavucontrol, it lists "HDMI/DisplayPort (unplugged)", which of course surprises me considering I'm reading it on my screen so it's not like the DisplayPort connection is unplugged.
I'm running Kubuntu 16.04, and currently making do my passing the audio out a USB sound card and then into a speaker, so it's not urgent, just . . . perplexing.