This little .dll pack will enable surround sound in S.T.A.L.K.E.R. Clear Sky, using OpenAL, that renders 3D sound and is compatible with the game.
S.T.A.L.K.E.R. Clear Sky - 5.1 Surround Sound Enabler:
1- It should be compatible with any mods.
2- To enjoy surround sound, make sure that you have OpenAL, that renders 3D sound and is compatible with S.T.A.L.K.E.R, installed (download from Openal.org).
3- Copy and paste "bin" folder into your game dir, overwrite files if asked.
4- Start up the game, there should be a new sound device showing up in the sound settings menu, called "DirectSound". Select that, enable EAX and restart the game.