Can you post output of "sudo aplay -L" You can test the sound with alsa directly with program speaker-test: http://alsa.opensrc.org/Speaker-test
probably it is included by default on ubuntu.
I have two AMD cards running sound through hdmi (ubuntu 15.10, archlinux and OpenELEC) with the default opensource drivers with DTS/AC3 pass through as well as 2.0 PCM sound to TV no problem.
How are the speakers connected... hdmi, line out, usb?
I haven't used regular Ubuntu, but in other versions the drill is to open sound settings and turn-off all devices except the one you are using. Turn them off, don't set them as fallback.
My work machine (an AMD machine) has the exact same issue, but only under 15.10. I tried everything I could for a few hours and gave up. I went back to 14.04 and everything was fine again.
Can you post output of "sudo aplay -L" You can test the sound with alsa directly with program speaker-test: http://alsa.opensrc.org/Speaker-test
probably it is included by default on ubuntu.
I have two AMD cards running sound through hdmi (ubuntu 15.10, archlinux and OpenELEC) with the default opensource drivers with DTS/AC3 pass through as well as 2.0 PCM sound to TV no problem.