I'm using my on-board soundchip with a S/PDIF output to a 5.1 sound kit. Trying to enable 5.1 sound, I followed these instructions : https://help.ubuntu.com/community/DigitalAC-3Pulseaudio
During the speaker test, everything works fine, I can hear sound from all my speakers. However, in practical test cases, for instance playing a movie in VLC, I generally get no sound, and in the rare cases I do, it's still stereo.
I ended up on this question that was asked a year ago, and never received any answer : Surround sound woes with 14.04
My problem is entirely identical. And indeed, keeping pavucontrol open does solve my problem too. Obviously, this is not a real solution.
I'd like to re-open this question : Does anyone know what causes this, and/or a decent fix or workaround that I can apply ?