Just unzip the packs of interest into your WoW Data folder and the zero-length files inside will mute the sounds in-game.
Note. As mentioned in the README, mutes from later versions of the game are likely to work for earlier versions, where those sounds exist.
Mute ALL Sounds Packs
The ALL Sounds packs for each WoW client are intended for those creating their own mute packs by deleting or selecting items from them. This saves the work of having to create many mutes individually.