The problem I've had was fixed in Intrepid; as far as I can tell it had to do with a changed default behavior of ALSA (hda-intel) to set the sound format of PCM output to float instead of integer, and this is what caused the spdif output to remain silent.
The Intrepid version of ALSA includes a mixer switch named "IEC958 Default PCM" which can be activated to set the default format to integer.
The problem I've had was fixed in Intrepid; as far as I can tell it had to do with a changed default behavior of ALSA (hda-intel) to set the sound format of PCM output to float instead of integer, and this is what caused the spdif output to remain silent.
The Intrepid version of ALSA includes a mixer switch named "IEC958 Default PCM" which can be activated to set the default format to integer.