Linux: sound output on speakers or headphones?

Buy a cheap splitter cable for two jacks. I'm in a similar situation used for a long time.

The cards are there.
About software switch, if I am not mistaken, Pulse can.
I apologize in advance, not too competent in this matter, but I hope that at least helped a little.

pulse easily handle it.
\r
plug any USB sound, which is supported by pulse. Well, on a situation — or gnome-volume-control (toggle the sound) or a pulse device chooser

see alsamixer (ncurses) and its variant without ncurses — amixer.

On some motherboards with integrated audio, a connector (brush) for the removal of nests front panel audio. Realacci driver (Venda) on my comp had the option to split outputs to both jacks were visible in the system as an independent device. The problem is that many programs are not designed for switching on the fly. Perhaps it can be solved with Virtual Audio Cable, but I do not have and do not intend the absence of windose.
\r
As for Linux in Ubuntu there's this, but it doesn't work — front and rear sockets are working as analog output, and when I choose headphones in both jacks are silent. Maybe Linux just doesn't work with my motherboard.
\r
Look at the specifications of your motherboard, maybe you will succeed.
\r
And in an extreme case, it is possible to solder a simple device that will change channels and they can be controlled programmatically.

and you can ask why you to software switch between headphones and speakers?
\r
Well, in the case, solve your problem in several ways:
in the forehead — buy the USB soundcard to it to pull up use, and in Ubuntu using pulseaudio/alsamixer to switch the audio output device.
the right decision — on all modern buildings have a front-panel USB and audio ports, so they connect to the motherboard and there poking headphones. if your zvukovojj firewood in Ubuntu complete plugging of the ears, the speakers themselves will varobacka. well, if you are not able then again through pulseaudio/alsamixer just cut down the channel columns/cut in the ears.
\r
if the second is not an option I would have just soldered a small cable to the switch, and through him, hooked up and speakers and ears.

At random, came to the following algorithm settings front panel audio:
1 Include PC
2 Run alsamixer (in a terminal enter alsamixer)
2.1 included headphone (press M)
2.2 expose the headphone to the max
2.3 close alsamixer
3 Plug the headphones to the rear panel
3.1 check if they work
3.2 if the work is repeatable, paragraph 2
4 Insert the headphones in the front panel.