TaxAkla: I use this wrapper to play some old games. Never tested with Giants but could deserve a test.
http://www.indirectsound.com/

chao-samu: Hi a little bit late, but i found a solution,

1. Save "Giants.exe" from GOG-Version (optional the "Bin" folder to - see below why)
2. Look for the offical "1.4 w/ EAX" Patch in the internet
3. Place the exe file of the Patch into the root folder of the Game (Default: "C:\GOG Games\Giants - Citizen Kabuto")
4. execute the Patch
5. Place the saved "Giants.exe" of the GOG Version back into the root folder (optional the "Bin" folder to)
6. Edit the desktop shortcut the field target from "C:\GOG Games\Giants - Citizen Kabuto\Giants.exe" to "C:\GOG Games\Giants - Citizen Kabuto\Giants.exe" -snd3d
7. Look into your ingame soundoptions if reverb and occulision works (if not be sure you installed a DS3D Wrapper like Indirectsound or Alchemy)

Note: The "Bin" folder contains updated textures in my opinion, the only files you need from the patch are "EAL" folder, old "gs_ds.dll" and old "gg_dx7r.dll". Haven't tested if grapic problems occur if you use the newer textures! Hopefully someone else can test it!