I took a look at Eiko's Boss rush... Well, that is definitly the easiest boss rush they released so far. Just bring Carbuncle, Summoner Spring II, and you can breeze through the 3 first battles. The last one? Zorn & Thorn, which is almost impossible to lose (it seems that Runic Blade even works against them). Really, free rewards.
Beatrix, who we will fight thrice, is something else entirely, but doesn't seem too hard either: all of her attacks (including Thunder Slash, though we may need to check this) are physical, so you only need to focus on DEF mitigation (ie. Power Break(down), Protectga, high-DEF equipment). And she can be slowed. It seems she will be very easy to beat with the Advancetaliate strategy (though her third fight may be a tad difficult, depending on how much damage one can deal before she uses Stock Break).
Oh well, my Sephiroth equipped with 4*+ Gladius (FFIX) should make short work of her with Advancetaliate. I can even equip him with the Self sacrifice materia. Add Armor Break(down) and/or Boost, Double Cut, and Beatrix should die very quickly.
Rinoa's event, on the other hand, is going to be a tad more difficult...