it really depends on the file, some files are very low volume, while others are loud, some require tweaking. what soundfile specifically are you trying to get to play, i could see if i could get it to play.
i have used RAW ambient_generics but most are very low volume...if you dot a couple around your map you will be able to hear them - even set at max. volume you will have difficulty hearing one.havent tested yet to see if these sounds will play on all clients yet though so...fingers crossed...