Comment 92 for bug 1332900

Node 0x02 [Audio Output] wcaps 0x41d: Stereo Amp-Out
  Control: name="PCM Playback Volume", index=1, device=0
    ControlAmp: chs=3, dir=Out, idx=0, ofs=0
  Device: name="ALC3661 Analog", type="Audio", device=0
  Amp-Out caps: ofs=0x57, nsteps=0x57, stepsize=0x02, mute=0
  Amp-Out vals: [0x40 0x40]
  Converter: stream=8, channel=0
  PCM:
    rates [0x560]: 44100 48000 96000 192000
    bits [0xe]: 16 20 24
    formats [0x1]: PCM
  Power states: D0 D1 D2 D3 EPSS
  Power: setting=D0, actual=D0
Node 0x03 [Audio Output] wcaps 0x41d: Stereo Amp-Out
  Control: name="Headphone Playback Volume", index=0, device=0
    ControlAmp: chs=3, dir=Out, idx=0, ofs=0
  Amp-Out caps: ofs=0x57, nsteps=0x57, stepsize=0x02, mute=0
  Amp-Out vals: [0x40 0x40]
  Converter: stream=8, channel=0
  PCM:
    rates [0x560]: 44100 48000 96000 192000
    bits [0xe]: 16 20 24
    formats [0x1]: PCM
  Power states: D0 D1 D2 D3 EPSS
  Power: setting=D0, actual=D0
Node 0x04 [Audio Output] wcaps 0x41d: Stereo Amp-Out
  Control: name="Headphone Playback Volume", index=1, device=0
    ControlAmp: chs=3, dir=Out, idx=0, ofs=0
  Amp-Out caps: ofs=0x57, nsteps=0x57, stepsize=0x02, mute=0
  Amp-Out vals: [0x40 0x40]
  Converter: stream=8, channel=0
  PCM:
    rates [0x560]: 44100 48000 96000 192000
    bits [0xe]: 16 20 24
    formats [0x1]: PCM
  Power states: D0 D1 D2 D3 EPSS
  Power: setting=D0, actual=D0

amp out/volume control is at the audio output,

preferred_dac pair is needed when you want the driver to assign THREE DAC to specific pin complex first and the other pin complexes share the volume control