I have the very same machine (Acer X1200).

I get sound by

sudo aptitude -y install build-essential libncurses-dev gettext xmlto xmltoman linux-headers-`uname -r`

sudo mkdir -p /usr/src/alsa
cd /usr/src/alsa
sudo wget ftp://ftp.alsa-project.org/pub/driver/alsa-driver-1.0.18a.tar.bz2
sudo wget ftp://ftp.alsa-project.org/pub/lib/alsa-lib-1.0.18.tar.bz2
sudo wget ftp://ftp.alsa-project.org/pub/utils/alsa-utils-1.0.18.tar.bz2
sudo wget ftp://ftp.alsa-project.org/pub/plugins/alsa-plugins-1.0.18.tar.bz2

sudo tar xjf alsa-driver*.bz2
sudo tar xjf alsa-lib*.tar.bz2
sudo tar xjf alsa-utils*.tar.bz2
sudo tar xjf alsa-plugins*.tar.bz2

cd alsa-driver*
sudo ./configure --with-cards=all --with-card-options=all
sudo make
sudo make install
cd ../alsa-lib*
sudo ./configure
sudo make
sudo make install
cd ../alsa-utils*
sudo ./configure
sudo make
sudo make install
cd ../alsa-plugins*
sudo ./configure
sudo make
sudo make install

sudo reboot
cat /proc/asound/devices
aplay -l  # will see device 0,3

sudo alsamixer  # unmute the IE958 entry
sudo alsactl store 0

#must do this as sudo... doesn't work yet as a paste..
cat > /etc/asound.conf << DELIM
defaults.pcm.device 3

Note, I never see any indication of HDMI with aplay -L, only with aplay -l

At that point, I can get sound by the Pref-Sound panel, switching everything to nVidia HDMI.

Also note that you appear to need 177.80 to get any sound, and 177.82 if you want 5.1.  I have personally rolled back to 173 b/c 177 kills Flash performance on the 8200, but 173 does not appear to support audio over HDMI (aplay -l shows the device, but no sound...), so I am using 173 HDMI video and the 6-ch analog outputs until I hear back from nVidia.

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