You can do that yourself, here's a brief tutorial :
Lobby Music :
Convert your mp3 songs to .ogg files and rename them as music01.ogg and music02.ogg, then replace them in the Sound\UI folder, If I'm, not wrong.
Sound Effects :
As for the killing sounds, convert your sound effects to .wav files and and rename + replace them in their respective folders, they should all be in the Sound folder, or _SG/Sound folder.
I might be starting a project, modding game sounds with other sounds from other games, if I'm bored.