I used the same strategy as Cyn, and I also used a stamina spring on each character (or whatever the item is that doubles your HP) just in case a Flare or a Perdition's flame caught me off guard. Using a light curtain or having your alchemist mix "wall" is also worthwhile to cut down on damage.

Also a cool thing you might not know: Since the boss steals your MP a lot, just let it. Keep your characters with 0 MP and then after a while Angra Mainyu will run out of its MP and then cannot cast Full-Life on its arms, and will spend every turn trying to get your MP with "osmose". Although it takes a good 15-20 minutes for it to run out of MP, once it does... the battle is easy-peasey. :moggie: