BIOS lists the internal speaker as an internal line-out. Change to
internal speaker + model=auto for better auto-mute capabilities.

Relevant alsa-info is here: 
https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/754964/+attachment/2002204/+files/alsa-info.txt

-- 
David Henningsson, Canonical Ltd.
http://launchpad.net/~diwic