Hello Vcube, are you trying to incite some System Shock chat here? 
I have nothing against it but frankly you will get more answers and readers over at  TTLG
The SBF-forums are mostly a base for up- and downloading Modifications and other System Shock related stuff.

That being said, I hope the sound experience with your Audigy card will make you want to play through SS2 another time. Or check out one of the fan-missions available here. I find Ponterbee station to be quite fun and it's made on a really professional level.

Cheers, Kolya

There is DeepFriedBeer's SoundUpgrade which changes most weaponsounds. I think it's quite good though I didn't like the new shipalarm too much. (Sounds like a submarine alarm.)
My GerMany Mod replaces the enemy talk with the equivalents from the German SS2-version. It's basically for regular players who have become tired of hearing the same old samples over and over again. I made it more or less for fun but it get's downloaded quite often.

You'll have to decide yourself if these mods are something for you. None of them is an "upgrade" as SHTUP is for graphics or Rebirth is for models. They are optional.
The reason why there is no universal sound-upgrade is that the sounds are what most people like about SS2, like you said yourself.

A mod you really should try when you played through SS2 too often to still get nervous is Zygoptera's RandomMod which randomly changes the places of loot, keycards, etc. and adds some very nice scripted events. Currently this mod is available for MedSci, Engineering and Hydro levels.

Kolya

That mod was combined with Arcaniac's model pack.
Look here: https://www.systemshock.org/index.php/topic,120.0.html