The default PulseAudio behavior is as follows:
First we connect something to the back panel of our MOBO, normally this would be speakers, then we connect something to the front panel, normally headphones.
In this case speakers would be muted and sound would go through headphones.
The question: How to configure things in such a way that would allow playing sound and volume control for both of the outputs separately
Making both outputs work at the same time is not hard, for that we need to disable "auto-mute" option in alsa-mixer (though not sure if it would persist after reboot).
However how to control their volume and optionally mute one of the outputs in software?
I've seen this or similar questions being asked a lot but so far I haven't seen a working solution. The best what I've tried so far is described here, but I failed to achieve any results using this information.
Note that I am not asking to play a different stream through these outputs, just control the volume. However if playing different streams is possible as well, it would be a great bonus!
The best solution from my standpoint would be to "teach" pulseaudio to treat front and back panels as separate output devices (which is possible on windows). But so far everything hints that this is not possible on Linux.
I am using Linux Mint 19.1, but this question should be relevant for all the ubuntu-family
On windows this operation is easily achieved by installing whatever realtek or your-soundcard-here drivers.