Every sound is shown in the importer. Their names aren't exactly descriptive. So you'll have to dig through them to locate the sound you want to replace.
From what I've been able to gather
The names with the numbers are commentary files.
The crowd, effects, menu sounds have somewhat descriptive names
The sounds played on the PA system(dismissal announcement or music) are named 1.wav
The background music in menu is named BL2008_48_24bit.wav. The sounds played during the intro videos are codemasters.wav and Transmission_games.wav respectively
There are 10963 sounds and I've only listened to a few of them so my assumptions could be wrong.
The filename for the menu music (not for ENG & AUS) is BL2008_48_24bit.wav
scroll the vertical bar to around 40% and you'll get that file
Or you could type bl when the focus is on the list view and the file will be selected.