For those who might still be looking for an answer to how this works, it is covered in the hints and tips by nickydude, a sticky on the forum. Basically, you set an entity outside your structure, and use this to attach a sound. Set the main script to repeatsound.fpi. Set the trigger zone main script to playerinzoneactivateused and the if used parameter to the name of the entity. Check out Nick's excellent guide for more detail.
I'm having some trouble getting multiple sound trigger zones in a levek to work - so let me know if you figure that one out.
'Yeah...I'm gonna' have to ask you to come in on Saturday. That'd be great.'