To be honest, I usually tell auditors "NO" when it comes to producing a full system ERD.  They usually don't have the need to know and it is a proprietary system.  I tell them to ask specific questions and then we'll be happy to give the table layout for that particular question including the first level of tables that any FKs may reveal.  They do not need to know the design of the entire database unless they auditing under a court order and search warrant looking for criminal activity or criminal neglect.