This was definatly not the best FM I've seen, and I think the guy was only rated about 1670.
Anyway, I'm finally figuring out how to counter it after a few losses myself and watching some expert recs.
This time around I made the right units.
Key point I think was when he underworld passaged me, but instead I put pressaure on his base with A/E and my army, so he never got a chance to send any units over.