MMW mentioned in the other thread that this is based on a hat worn by the protagonists of "The Way to Eldorado". It's actually "The Road to El Dorado". "El Dorado" is, of course, the mythical city known as "the Golden One". In Spanish, "the Australium One" would just be "El Australium" (based on how TF2 translates "Australium" into Spanish), not "El Australio", and "El Australium" doesn't really flow off the tongue. There also doesn't appear to be very much Australium in this headdress, so it's kind of weird unless you get the reference.

Now, as a fluent Spanish-speaker, I would recommend renaming this headdress to either "The Road to El Tocado" or "The Road to Los Tocados". "Tocado" means both "headdress" and "headgear". It also works as a play on words, because "tocado" is also colloquial for "not all there" (in terms of brains), so "el tocado" could also literally mean "he who is somewhat mentally unbalanced", which is pretty descriptive of all of the mercs.