I have a strange bug where gunfire particularly is muted, you might hear the first shot, but then nothing, while impact sounds and other effect sounds are present.
Looking at the console (Alt+ctrl+~) When I fire my weapons, it shows an error that there's some unknown command being executed (snd_3d & snd_eax or something very similar) but I don't know the real commands for those functions, they do not exist in the main menu options or in the environment.cfg, and, frankly, the internet is almost completely dry of a proper list of functional commands that you could enter into the console or the environment.cfg config file.
I have the GOG version, and a strong laptop (intel quad core i7 2.5ghz, 12gb RAM, Nvidia GT 840m, Win8) The sound systems list something like Realtek HD plus a Nvidia virtual audio device.
Any help would be appreciated!

Update:
I found out that typing "help" into the console reveals a bunch of very interesting looking commands. Unfortunately, they didn't seem to be in much of an order, as I scrolled the list with PgUp + PgDown, and then the list got cut off, probably by some console history show limit.
I tried the two sound related commands I spotted, snd_mix_reload & snd_mix_autoreload, but they did nothing.
There's a lot of potential with tweaking these commands, but I'm not much of an expert on fishing them all out and testing them.

Try disabling EAX/Hardware acceleration in the sound options.

Not an option in the game menu like I said, also not in my Control Panel Realtek settings or the basic windows sound system properties.