I just beat Soul Shrine. That was a ton of fun, though not super hard. The hardness comes from the fact you can't save, so if you die you waste all the progress you've made. But if you keep in mind what all the enemies do, it's not bad. Just remember which ones have instant death attacks, etc.
The last few waves have all the bosses from Kefka's tower (except Kefka and his statues - /cry I wanted more Lightbringers 😃) and then the last one are all the dragons in Dragon's Den, ending with Kaiser.
The Glutturns suck though. They are not hard, as they only require you feed them items (i.e. Hi-Ethers, etc). But they have some awesome steals, and unfortunately if you don't feed them the items they just decide to start 1-hit KOing people at random. I was only able to steal from one (the first time I tried to outlast them I lost my whole party and had to start over -_-), but I got a Soul of Thamasa so now I have two! w00t! I also have two Master Scrolls because that guy shows up again and drops it 😃
I had been leveling my main party in the Dinosaur Forest and picked up like, 3 Celestriads from Brachiosaurs. I got pretty lucky. I have Locke, Terra, Celes, and Mog at lvl 99. Locke has the Lightbringer/Paladin Shield and maxed speed so he can just about steal anything. Terra has a Soul of Thamasa and Celestraid with maxed magic...thats self explanitory. Celes has high strength and magic and genji gloves two Atma Weapons with a master's scroll. Mog has maxed strength with Dragoon boots and Dragon horn. My party does damage like nobodies biznotch. I'm working on a secondary party right now with Edgar, Cyan, Sabin, and Shadow. They're only around lvl 40 right now. I haven't gone into the Dragon's Den yet, but I have a feeling that when I get done power leveling, I'll have little to no problem.
Yeah. An 8 hitter with AtmaWeapons is pretty unforgiving. Kaiser doesn't have enough HP to stand up to much of that. Your characters' ATB bars will be having plenty of time to fill up while he wastes his time doing that long, slow, barrier change.