just to use the soundscapes already there?
put an env_soundscape entity in, adjust the distance (you'll see the big yellow sphere) whenever a player is inside this sphere they will hear the soundscape played by that env_soundscape, and infact they will hear it untill the enter another env_soundscape's sphere
Then you want some places for the sound to be played, these are info_target entities, they all need unique names (I think, think mind you, I havent tried this: you can have several info_targets with the same name and the sound will play though all of them) then in the env_soundscape there is a "play sound from" or something similar and you put the names of the info_targets in there.