I forgot to mention that the "headphones" volume was not changing anything, however the main and PCM volumes were modifying the headphones and speakers volumes at the same time.
A little workaround to have only headphones working, put:
options snd-hda-intel model=6stack-dig
at the end of /etc/modprobe.d/alsa-base
reboot
then in the tool to control the volume, go in parameters and uncheck "headphones" (checking/unchecking will change what is working: speakers/headphones), that did it for me.
I forgot to mention that the "headphones" volume was not changing anything, however the main and PCM volumes were modifying the headphones and speakers volumes at the same time.
A little workaround to have only headphones working, put: d/alsa- base unchecking will change what is working: speakers/ headphones) , that did it for me.
options snd-hda-intel model=6stack-dig
at the end of /etc/modprobe.
reboot
then in the tool to control the volume, go in parameters and uncheck "headphones" (checking/