Does the MacBook Air Support 5.1 Surround Sound The title pretty much says it all.  I have a 13" version of the newest-generation MBA.  Can I get 5.1 surround sound?  If so, do I have to do anything special to enable it?
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.