Unless you are starting your DONE4 in USA (and not recommended since much more expensive than starting elsewhere, even compared with Australia), this is not a good idea. If you issue by US agent, you then have to pay the higher of the price at origin or price at country of agent. US price is higher than pretty much anywhere so that is the price you would need to pay.
What NM (and others) is suggesting is when you book with either airline or TA located in your departure country, you get them to issue on AA ticket stock. Obviously the only airline that will do that is AA. However travel agents generally have flexibility to issue on any airline that is included on the DONE4 itinerary (ie AA will be one of them). Some TAs may prefer to use QF but strictly there is no need to.