Custom Sprays
Transparency
Animation
Custom Sounds
Adding & Replacing
Modifying
Customising Sounds Within CSS
You need GCFScape to unpack the .gcf files to edit them for your game.
Before we get started i want to admit to not knowing how to change the death sounds (dominating, rampage etc). This only changes automated sounds (hostage screams, enemy spotted). Each sound is put into the folder necessary you can extract them all with GCFScape. You must extract all the text files from counter-strike source shared.gcf . Once this is done you'll find it in C:\Program Files\Valve\Steam\SteamApps\<your name>\counter-strike source\cstrike\scripts.
Now each text file holds information about the sounds played during the game. Death sounds and quakes can be changed your end but no-one will ever hear them apart for you. Each script routine in the files has an event, attenuation, pitch, volume and files used. You can modify all of these to give your CSS that little tweak no-one else has but lets face it all you need is attenuation, volume and files.
The game_sounds file has they volume system aliases you need with comments so you know what is what. Print it out and use some brain power and you'll have your sounds modded and running smoothly within 20 mins.