Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
yes - as long as the speakers have optical input, as the headphone socket can also output optical digital (and therefore 5.1) audio
 
You will need to purchase a mini toslink dongle to connect your 5.1 receiver to the digital out headphone jack on the MBP.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.