Comment 34 for bug 878986

The ALC883 series 7.1+2 Channel High Definition Audio (HDA) codecs are compliant with Microsoft's UAA (Universal Audio Architecture). The ALC883 series provide 10 DAC channels that simultaneously support 7.1 sound playback, plus 2 channels of independent stereo sound output (multiple streaming) through the front panel stereo output.

there is no hareware control which allow you to mute the front panel and rear panel since they can play different stream