When in September I was using ArchLinux, I remember that pulse audio It was updated from version 0.9.23 to 1.0, until the previous version every time I connected my headphones to my laptop (HP Pavillon DV6) I could choose if I wanted the sound in the headphones or in the speakers, but from version 1.0 already I couldn't mute the speakers from kmix.
The problem was that I was the only one who used Arch who realized (or suffered) that ... until at the end when the new Ubuntu, in the English forum I found the solution to my problems, so I adapted that solution for my Arch.
If what we are looking for is that every time we connect the headphones, the speakers of our laptop are automatically muted, just do the following:
We open the terminal:
1 - We type: sudo su
2 - Then we write: kate /etc/modprobe.d/modprobe.conf
Inside kate we will write:
options snd-hda-intel enable_msi = 1
options snd_hda_intel model = hp-dv5
Once this is done, we will have the problem solved.
I hope it helps you, these same lines will also help you alsa.