So what you are saying is that you want an announcent system? Like, instead of just a hud message, it will make the vox guy say something after that too?
If that IS what you are aiming towards then you would be somewhat limited, the vox guy can only say a select list of words.
http://tf.valve-erc.com/kbase.php?id=23
Is the most complete list I've found.
EDIT: There is a way to sort of manipulate what the words say by cutting them off or starting them late, but I forgot how to do it.