Comment 24 for bug 1264665

For digital audio, if an HDMI device supports audio, it is required to support the baseline format: stereo (uncompressed) PCM. Other formats are optional, with HDMI allowing up to 8 channels of uncompressed audio at sample sizes of 16-bit, 20-bit and 24-bit, with sample rates of 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz and 192 kHz

if your other computer only support stereo, they don't need any speaker allocation

Node 0x07 [Pin Complex] wcaps 0x40778d: 8-Channels Digital Amp-Out CP
  Control: name="HDMI/DP,pcm=8 Jack", index=0, device=0
  Control: name="IEC958 Playback Con Mask", index=2, device=0
  Control: name="IEC958 Playback Pro Mask", index=2, device=0
  Control: name="IEC958 Playback Default", index=2, device=0
  Control: name="IEC958 Playback Switch", index=2, device=0
  Control: name="ELD", index=0, device=8
  Amp-Out caps: ofs=0x00, nsteps=0x00, stepsize=0x00, mute=1
  Amp-Out vals: [0x00 0x00]
  Pincap 0x0b000094: OUT Detect HBR HDMI DP
  Pin Default 0x18560010: [Jack] Digital Out at Int HDMI
    Conn = Digital, Color = Unknown
    DefAssociation = 0x1, Sequence = 0x0
  Pin-ctls: 0x00:
  Unsolicited: tag=03, enabled=1
  Power states: D0 D3 EPSS
  Power: setting=D0, actual=D0
  Connection: 0
  In-driver Connection: 3
     0x02 0x03 0x04