joro@debian64:~$ amixer sget PCM
Simple mixer control 'PCM',0
  Capabilities: pvolume pswitch pswitch-joined
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Front Left: Playback 9 [29%] [on]
  Front Right: Playback 9 [29%] [on]

Note the "[on]". Check if your output is similar.