This mode allows an output stream to have two substreams, one for the
speakers and one for the headphone.  Each of the substreams has independent
PCM data and uses a different DAC.
Signed-off-by: Harald Welte <HaraldWelte@viatech.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>