I have made a pack file that fixes the sound corruption for especially mods.
Now how did I accomplish that?
First, credit to crux3D and his symphony de-compiler and re-compiler. Without it, I could never fix the issue.
Now the tool of symphony does work with S2TW, but the main issue is (was) that many fields where unknown. So, what I did, is I compared the file with NTW (same engine and code).
The main reason that sound becomes corrupt when for example adding new units, is that the sound_bank_projectile (it looks for information in the db => projectiles: gun_type and shot_type table)was unit specific, while in NTW it wasn't.
So I deleted all unit specific lines in the sound_bank_projectile and re-compiled it. And after testing, the sound (firing) was normal. No more weird sounds when firing guns, bows, rifles, etc...
This sound_fix.pack file can be used for ALL mods. Just see that other mods, don't have any sound_packed files in their mod packs.
Just add the sound_fix.pack in your data (Usually found in C:\Program Files (x86)\Steam\steamapps\common\Total War SHOGUN 2\data) folder and activate in modmanager.
Enjoy.