Does Mac OS X Lion support surround sound on optical audio outputs?
The optical output (Mini TosLink) does support multi-channel sound, up to I think 7:1 - but the standard 2.5mm doesn't.

iffi9211
Re: surround sound
Jan 30, 2012 2:49 PM (in response to parker612)
I was able to fix this problem, my speakers are connected to my pioneer receiver and I used it to create surround sound. iMac has toslink output which is connected to my receiver. iMac however gives only 2 channels and doesn't have option for surround sound on every track. It will not create surround sound from mp3 songs like some sound cards can. However if I play dvd that has surround sound then iMac will output 5 channels.

Thanks for the reply.
Edit: second post down here explains it.