Comment 76 for bug 1040873

Well, upstream now has a subwoofer quirk for your machine, so this should fix the alsa level if you install the latest drivers ( https://wiki.ubuntu.com/Audio/UpgradingAlsa/DKMS ).

Then the PulseAudio stuff remains, where my recommendation is to add the stuff as suggested here:

https://<email address hidden>/msg08737.html

I e, you should add this section in /usr/share/pulseaudio/alsa-mixer/profile-sets/default.conf and extra-hdmi.conf :

[Mapping analog-surround-21]
device-strings = surround21:%f surround40:%f
channel-map = front-left,front-right,lfe,lfe
paths-output = analog-output analog-output-lineout analog-output-speaker analog-output-desktop-speaker
priority = 8
direction = output