Jafdet's War Atmosphere
Jafdet's War Atmosphere is what seems to be a later version of the Expanded Soundpack that includes engines, voices, etc.
I personally use the Weapons, Hits and the engine sounds from the folder labeled "CombineJagdt+"
1. COPY your entire Audio folder to res_mods/version#/ 2. Drop new sound files into that folder and overwrite the existing files.
If you do not copy the rest of your audio files they will not play in game.