I run Ubuntu Linux (Natty as of this posting) and there is a known bug in which the digital output (COAX) would somehow go out for analog sound. This always pissed me off and the only cure was to do a hard reboot. Well, after perusing the forums and bugs lists, I found a cure!
Basically, when you notice analog sound output going out, you have to run this command a few times until you see some Segmentation Faults (trust me it’s ok):
# cat /dev/urandom | ac3dec -R
Once you run this, however, I noticed the SPDIF OUT would be suddenly turned on and thus the coax output would not work still. Easy enough to fix by going into alsamixer and unchecking the SPDIF output and voila, you should hear analog sound again!
I currently have the Logitech Z-5500 Digital sound system connected to it so I can tell when analog is working when it shows up as Stereo x2 rather than No Output Detected.
Hopefully this helps someone!