solved sound issue on my ASUS G51VX. i finally figured it out. i'm not sure if this is true for all ASUS G51VXseries but mine the sound card would not work while running the 32 bit version of UBUNTU which is "recomended" when you are at the download screen. Any way, i tried installing the 64 bit version just to see what would happen. Than using the command "sudo nano /etc/modprobe.d/alsa-base.conf" in the terminal box to access the manual parameters for the alsa drivers. At the bottom of the page i added "options snd-hda-intel model=asus-mode3" (i tried all other options and this one seems to work the best). and than rebooted the computer and sound was back on both the outside speakers and the headphones.
-the 32 bit version of ubuntu did NOT work with the soundcard in my ASUS G51VX, ALC663.
-installed the 64 bit version of UBUNTU
-in the terminal box insert.
" sudo nano /etc/modprobe.d/alsa-base.conf "
-scroll down to the bottom of the page and insert the following command after the last command already there.
" options snd-hda-intel model=asus-mode3 "
-this one worked for me but you could try one of the other models ("asus-mode1" through "asus-mode8", or either "base" or "auto")
-exit saving your changes by holding down the "Ctrl" and "Shift" keys and pressing the " ^ " key (6) and than the "x" key.
-it'll ask you if you want to save your changes press "y" and than "Enter" to save the changes to the document.
-you'll find your self back in the terminal box. Now reboot your computer.
I really enjoy using UBUNTU so hopefully this little bit of info helps and if it doesn't don't get discouraged, the night is darkest just before the dawn.
Best of luck to everyone.