The only way that I've ever been able to beat the Iroquois FF as an Aztec -- Scouts. Scouts as far as the eye can see. Take a look -- it's interesting to see just how well this very, ahem, "special" unit can do against the Iro FF when the situation is right.
In this recording, I use a build order that lets me boom and spam Scouts at full speed. It's a good one for when you're comfortable that you'll have plenty of time to work with.