currently you will need to use character sound sets for this as you can only specify 1 or 2 sounds per object.
so you can't use a zone directly but you can tell the zone to play the sounds linked to a character with those sounds
inside audiobank is a character folder, you need to create a new one and copy the format from the others, place your sounds inside one of the folders (i recommend sticking to the ones that are used by the stock entities - such as onAggro or onHurt)
name your files 0.wav, 1.wav, 2.wav etc
now set a character which calls this folder in it's script's init(e)
SetCharacterSound(e,"name of folder inside character folder")
then place your zone and tell it to play the sound from the desired folder and character
PlayCharacterSound(*character entity number*, "name of folder inside your own folder - onHurt etc")
it will automatically pick one at random i believe
life\'s one big game
windows vista ultimate
i5 @3.3ghz, 4gb ram, geforce gtx460, directx 11