All these games support surround sound.
The right question is: what sound card do you have? Very few sound cards support Dolby Digital Live (and none support DTS Interactive as far as I know); currently, those that do use the same chip as the new 'HD Audio' Intel motherboards, but they do a lot of processing in software and therefore can slow down your games.
The old nVIDIA nForce motherboards (1 and 2) and XBox, which is an nVIDIA motherboard, had built-in soundcards that could do Dolby Digital Live, but they stopped that - it's not available on nForce 3 or 4. (I'm guessing the licensing fees to Dolby were too expensive.)
Some sound cards advertise 'Dolby Digital.' This means they will pass through the Dolby Digital stream directly from a DVD to the spdif output of the soundcard. It does NOT mean it will do real-time encoding of whatever game you're playing to a Dolby Digital signal - that's called Dolby Digital Live, previously known as Dolby Interactive Content Encoding (DICE).
Another option is the recently announced Creative DTS-610 which is a box with 6 analogue inputs and a digital out; it implements DTS interactive, albeit with a delay of up to 50ms.
Yet another option, although this one I'm not 100% sure about: The Creative Audigy 2 cards will output three PCM digital streams, each stereo, giving you your 5.1 channels. But I don't know of an amp which will treat 3 channels of PCM as a single input.
Ignoring any form of Dolby/DTS, the game will use however many speakers you have plugged in and your soundcard supports.