PulseAudioはSPDIF出力をステレオではなくモノラルとして認識します。

Archlinuxを搭載したCubietruck ARMボードでは、pulseaudioはステレオ/2チャンネル受信機の代わりにモノラル受信機を生成します。

Card #1
    Name: alsa_card.platform-sound
    Driver: module-alsa-card.c
    Owner Module: 22
    Properties:
        alsa.card = "1"
        alsa.card_name = "On-board SPDIF"
        alsa.long_card_name = "On-board SPDIF"
        alsa.driver_name = "snd_soc_simple_card"
        device.bus_path = "platform-sound"
        sysfs.path = "/devices/platform/sound/sound/card1"
        device.form_factor = "internal"
        device.string = "1"
        device.description = "Built-in Audio"
        module-udev-detect.discovered = "1"
        device.icon_name = "audio-card"
    Profiles:
        output:analog-mono: Analog Mono Output (sinks: 1, sources: 0, priority: 700, available: yes)
        off: Off (sinks: 0, sources: 0, priority: 0, available: yes)
    Active Profile: output:analog-mono
    Ports:
        analog-output: Analog Output (priority: 9900, latency offset: 0 usec)
            Part of profile(s): output:analog-mono

Alsaを直接使用するとうまく機能しますが、この問題の原因は何ですか？