After my later adventures with getting sound out of the jack with the Cubieboard 2, I thought I fixed the main audio issue, but I've hit another one: there is very annoying buzzing sound that comes out after exactly 5 seconds of not playing anything. And it's not like a it's a discrete static white noise, no no, it's more like garbage amplified to a high volume. If I start playing something again, the noise stops.
I have absolutely no idea where to look in order to fix that issue. Re-muting the channels and lowering down the Power Amplifier to 0 doesn't help at all (no influence on the resulting buzzing).
As a side note (but I should probably open another ticket), I'm unable to make it work with pulseaudio, or make applications consider the Power Amplifier channel as the master channel for volume control with ALSA (so apps can't change the volume).