It helps a TON if you cast Guardian as soon as possible to lower damage to a few of his attacks.* Also, it helps equip Fire rings to all of your characters, so when he uses his fire attacks they'll heal you. Another tip: Love Song works on Omega apparently, though I have yet to try it myself. I will definately try sometime today, though.
*Blue Magic. You can learn it from a Stingray in the waters just south of the sunken Walz Tower.
Edit: Mmm...I just pwnd Omega. None of my characters are even at level 50 yet, either. My party consisted of a Blue Mage, a Bard, and two Sword Mages.
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