@Zaverel, What do you mean by "It's not perfect but that work" ?
it's cpu extensive because all audio is recoded in ac3.
You can try with this in /etc/asound.conf (for global user ) or ~/.asoundrc (only user)
pcm.!default { type plug slave.pcm surroundaudio }
ctl.!default { type plug slave.pcm surroundaudio }
pcm.a52encode { type a52 format S16_LE channels 6 rate 48000 bitrate 448 }
pcm.surroundaudio { type upmix slave.pcm a52encode channels 6 }
and start xine with --audio=alsa:surroundaudio