After Enslaved released a little surprise is lack of 5.1 sound. Now Namco announces an upcoming update to fix it.
This affects only users who have sound system output via optical cable. Over HDMI it is currently support 5.1, if you have activated the PCM channels in the sound settings.
There is no exact date for the update annnounced yet, but Namco confirmed to Joystiq that, it is to appear in the next few months with DLC release.