I used the same strategy as you did against the Omega Weapon, except I had X-Fight along with 2 swords and Bolt3 magic sword.

For Shinryu, I equipped everyone with Coral Rings to absorb Shinryu's Tidal Wave attack. Then I had my main attacker equipped with 2 swords, X-Fight and time (dimensional) magic. I had another character with summon, X-magic and time magic. First, I had the main character use Quick and then X-Fight twice (totally 16 attacks), the other character use X-Magic with Haste2-Quick-Bahamut-Bahamut-Bahamut-Bahamut combo. After this, I had the remaining characters heal the party as well as they can, and finally I had the main attacker use another Quick with X-Fight twice after that. This finished off the dragon.