Sounds like you have the same problem we have here, though in the opposite direction. Our fresh install of 12.04 32 bit won't let us switch from digital output to analog. Default will go to analog only if no other sound card hooked up (ie remove USB headphones).
There is an option in
pavucontrol to select between digital and analog outputs but it is not recognized by the default volume control and multiple outputs are not possible (application switching between streams is disabled).
Try pavucontrol and see if you can access the additional configuration there?
Alternatively you can do the configuration with
pactl via terminal, see the manpage for more details. Also you should check the
alsamixer settings in terminal, sometimes you try searching the root cause in pulseaudio, while its alsa instead.