I have the same question. I would love to output SPDIF through the D/Port.

Currently have Ubunu 10.04 installed.

I was able to generate the following from the System testing application:

Node 0x08 [Pin Complex] wcaps 0x430681: Stereo Digital
  Pincap 0x00010024: IN EAPD Detect
  EAPD 0x0:
  Pin Default 0x40c003fa: [N/A] SPDIF In at Ext N/A
    Conn = Unknown, Color = Unknown
    DefAssociation = 0xf, Sequence = 0xa
    Misc = NO_PRESENCE
  Pin-ctls: 0x00:
  Unsolicited: tag=00, enabled=0
  Power: setting=D0, actual=D0
  Delay: 3 samples
Node 0x09 [Pin Complex] wcaps 0x400301: Stereo Digital
  Pincap 0x00000010: OUT
  Pin Default 0x0144131f: [Jack] SPDIF Out at Ext Rear
    Conn = RCA, Color = Black
    DefAssociation = 0x1, Sequence = 0xf
    Misc = NO_PRESENCE
  Pin-ctls: 0x40: OUT
  Connection: 2
     0x05* 0x0a
Node 0x0a [Audio Selector] wcaps 0x30090d: Stereo Amp-Out R/L
  Amp-Out caps: ofs=0x00, nsteps=0x0f, stepsize=0x05, mute=1
  Amp-Out vals:  [0x80 0x80]
  Connection: 1
     0x0c
Node 0x0b [Audio Selector] wcaps 0x300105: Stereo Amp-Out
  Amp-Out caps: N/A
  Amp-Out vals:  [0x1f 0x1f]
  Connection: 1
     0x07

Now I'm not a Linux expert by *any* stretch. Can anyone decipher this?