Comment 2 for bug 1227795

ftp://download.nvidia.com/XFree86/gpu-hdmi-audio-document/gpu-hdmi-audio.html

but ad1989b is your on board sound

Node 0x1b [Pin Complex] wcaps 0x40030d: Stereo Digital Amp-Out
  Control: name="IEC958 Playback Volume", index=0, device=0
    ControlAmp: chs=3, dir=Out, idx=0, ofs=0
  Amp-Out caps: ofs=0x27, nsteps=0x27, stepsize=0x05, mute=1
  Amp-Out vals: [0x00 0x00]
  Pincap 0x00000010: OUT
  Pin Default 0x0145f1a0: [Jack] SPDIF Out at Ext Rear
    Conn = Optical, Color = Other
    DefAssociation = 0xa, Sequence = 0x0
    Misc = NO_PRESENCE
  Pin-ctls: 0x40: OUT
  Connection: 1
     0x02

Node 0x1d [Pin Complex] wcaps 0x40030d: Stereo Digital Amp-Out
  Control: name="HDMI Playback Volume", index=0, device=0
    ControlAmp: chs=3, dir=Out, idx=0, ofs=0
  Amp-Out caps: ofs=0x27, nsteps=0x27, stepsize=0x05, mute=1
  Amp-Out vals: [0x27 0x27]
  Pincap 0x00000010: OUT
  Pin Default 0x1856f1b0: [Jack] Digital Out at Int HDMI
    Conn = Digital, Color = Other
    DefAssociation = 0xb, Sequence = 0x0
    Misc = NO_PRESENCE
  Pin-ctls: 0x40: OUT
  Connection: 1
     0x0b

http://www.asus.com/Motherboards/P5Q_Deluxe/#specifications

Internal I/O Connectors

1 x S/PDIF Out Header

P5Q Deluxe user maual

14. Digital audio connector (4-1 pin SPDIF)

do you mean you are using the internal spdif out header ?