Last night we got wiped bad on Tholuxe Paells...60 of us. Yeah, I know, 60 people should be able to drop her easy. Here's what happened. Our raid leader was a melee, so he ran in with the melee. He died immediately so instead of someone calling in the casters all at once, we waited about two minutes before trickling into Vox's lair. She got down to 10% the CH'd herself. I starfire'd her, she resisted, her breath hit me for 15, 45, and 250 at 199 CR. I decided it was time to gate back to safe hall (only one other guy in there with me), but she summoned me and ate me.
Have your melee run in and start pushing her all around the lair so she can't cast. NEVER let her get on the rocks or the wall b/c then you can't push her and she will CH. Have one raid leader (or more) inside the lair coordinating things in there and one in the safe hall coordinating the sending in of the different groups. Then he should go in once everyone else is in.
Just keep pushing her around, and maybe allow three or four mages to summon air pets and give them two gnoll hide lariats to help interrupt Vox's casting.
Always have levitate or DMF on. Those polar bear pits aren't any fun at all, and CR from the pits is awful. During your CR remember that an Ice Giant does spawn in the safe hall, so be sure to rez a few tanks along with the Rogues and clerics. Once you get at least one Rogue rezzed the CR begins in full force. Alternate between dragging out Rogue bodies and Cleric bodies. Then tanks, then Necros (in case summoning is needed) then all others.
Always keep one cleric in the safe hall while Vox is getting taken down. It isn't much fun for them (though certainly safer), but CR is impossible without one cleric (unless you want to use one charge on someone's Staff of Forbidden Rites) still alive to Rez. Good luck, and drop that ugly mother.