mplayer -ao alsa:device=hw=0,alsa:device=default, -ac hwdts,hwac3, <file>

Config file: ~/.mplayer/config

# audio output and codecs (priority list)
ao="alsa:device=hw=0,alsa:device=default,"
# try to use first hwdts and then hwac3
# the trailing ',' stands for fallback to any not listed codec
ac="hwdts,hwac3,"

In ~/.xine/config

audio.device.alsa_passthrough_device:hw:0
audio.output.speaker_arrangement:Pass Through