I just beat Byrnhilda, what I did was set Sazh and Vanille as Ravagers, then when hp got low, had SAZ spam potions with Doctors code on. Then swapped to WAR and Peace when things got hairy, then swapped back to Dualcast, to build up Byrns chain bar quite easily.
Gamer Tag: TT LuckyUrDead No one cares about you Magus, you're like the Zoidberg of our little forum group. ~Aimuko~
Sazh and Vanille both chain --> Sazh chain and Vanille heal --> found out about buffing allies so has Sazh buff and Vanille chain --> switch to heal when needed or both chain when no buffs left to cast