Does the MacBook Air Support 5.1 Surround Sound
Not natively, no. The headphone jack is a standard TRS with no optical component.

You can buy a USB sound "card" with 5.1 audio output such as this one:

http://www.amazon.com/Zalman-ZM-RSSC-External-Sound-Card/dp/B0001OZ2K8

That's just the first one I found, so a little more market research might be in order. Something similar to it should get the job done though.