basically I would make sure your people + aeons are at overdrive, go in and cast hastega (cause he's fairly slow), shell and if you want a measure of safety auto-life on at least one person. Shell helps dampen his magic attacks A LOT. Anyway, then make sure you have Kimahri lancet him to learn Nova and start hitting him with your overdrives and the aeon overdrives. Since I found it damn near impossible to get the Magus sisters up to overdrive I had Yuna grand summon them. I had him dead using this strategy, saddly about half a second after he started dying, we had a power outage.... I was REAL happy, and now I get to do it all again *grr*
You want to make sure your people are at good levels though, if they're not even far enough to have auto-life and the like, you may just want to run around the dungeon a little more ;-) Good luck!