Windows has support for analog surround out of a soundcard. This is used by games to support surround. Mac OS only supports the pass-through of encoded digital surround streams via the digital outputs and there has never been a game that utilises this method as it requires an encoding of the audio stream that might cause performance issues.
Some games do there is a thread on this forum about the games that do use multi channel audio and what games have been tested it's worth a read if you are interested in it.