How to make the internal subwoofer work on an Asus G73JW?

It is very unlikely that a bug was fixed a year ago, was provided with up-to-date drivers from the ubuntu-audio-dev ppa, but did not make it for the release in 12.04. LTS.

Therefore I suggest you first have a look whether your /etc/pulse/daemon.conf is set to enable 2.1 sound. There should be the following entries:

default-sample-channels = 3
enable-lfe-remixing = yes

Try if that helps you to get sound to your subwoofer before you take efforts to intall possibly unstable new drivers.

At present there are no newer drivers than those installed by 12.04 available from the audio-dev-ppa (1.0.25+dsfg-0ubuntu1). This may change however in the near future. According to the release notes for ALSA drivers custom kernel modules need to be built from source:

A custom alsa-modules package can be built from the sources in the alsa-source package using the m-a utility (included in the module-assistant package). ^{release note for alsa-base}

After trying the changes on /etc/pulse/daemon.conf without success, I added to etc/modprobe.d/alsa-base.conf this line at the end:

options snd-hda-intel model=asus-mode4

Now it's working perfectly!