The level indicator in the screenshot

does jump around even if nothing is playing. The indicator also reasonably represents sound levels when music is playing. I dont have any mediaservers running or noisy browsertabs open. Also no mic connected. When I turn the volume to max in software and on the amp, there is no noise from the speakers at all. Played music is loud and not distorted.

Hardware: Realtek ALC889 over optical audio connector to a generic amp.

Software: Debian Wheezy with latest backport kernel 3.14 (same thing on wheezy 3.2 stock), wheezy pulseaudio, xfce session, a custom asound.conf that enables pulseaudio to push sound over optical port.

/etc/asound.conf

pcm.a52 {
  @args [CARD]
  @args.CARD {
    type string
  }
  type rate
  slave {
    pcm {
      type a52
      bitrate 448
      channels 6
      card $CARD
    }
  rate 48000 #required somehow, otherwise nothing happens in PulseAudio
  }
}