Hi guys. Installed MX15 on a machine I just built. Installed all the Nazi codecs, adjusted ALSA and Pulse as needed. Had Youtube going fine and went to Clementine. No sound and no sound in Skype. Screwed around a little and decided to dig around in the BIOS.
Gigabyte board.
Disabled local sound.
Waallah !
What happens is the HDMI setup seems to override"system" and takes care of the audio when the local was disabled(was set to auto) in the BIOS.
Dunno if it works outside of Gigabyte boards.
If sound is screwing with you, go look in your BIOS.

My guess is either way, disable and use your softwarez to choose and adjust sound.
Automatic is for bed wetters anyway. Do it YOUR way.
That's why we're here and not running an Apple, right ?
Man this bear screams. 2GB video, 16 GB memory. SSD(2 gb swap), 3.7 i4, 32" LCD TV-monitor rig.

First upgrade since 2006. The old horse is still plenty fast with MX.
2.0 Celeron, 2gb mem, 21" LCD.
I just felt the need to go 64 bit and SSD. I figure I'm good for another ten years. More worried about ME being running than this machine.
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Glad you like what you see with mx-15!

I also have run afoul of hdmi settings. In my case though pulseaudio chose the the HDMI rather than the speakers. I just disabled the HDMI profile in pulseaudio and I was good to go.