Headphones not working in Kubuntu 16.04

I'm trying to set my new Kubuntu 16.04 system on a Alienware 15 R2 laptop. The speakers and usb headphones work properly but the headphone jack is not detected.

I have done some research about it and some people suggest to do some changes in the /etc/modprobe.d/alsa-base.conf configuration file.
I have tried to add the lines:

options snd-hda-intel model=dell-alienware
or
options snd-hda-intel model=dell-eq

but it did not change anything after rebooting. Also by executing alsamixer I have unmmuted all the options (however I did not see any option for headphone jack). Also I have installed pavucontrol but this software does not display any headphone jack option either.

Thanks for your help!