Unfortunately, getting the Myth chest first was a costly mistake and you don't really have any good options to bring yourself up to where you need to be. There are, however, 2 ways to do it.

1: Bite the bullet. Get the DL cowl and use it until you can buy enough other Myth gear to cap yourself.

2: Crafted gear and food. The Vanya hat can be melded with up to 12 Acc and would be the best bet considering it only takes 9 Philo and replaces an AK piece. The 2nd piece is a bit of a toss up. Chest, Gloves, Ears, and Rings are out leaving Waist, Legs, Boots, Neck, and Wrist. Of these, only the Waist and boots cost 9 Philo mats; the rest are 18. Get both pieces crafted, cap them on Acc using materia, and eat good food. All told you are probably looking in the ballpark of 800k - 1mil+ fro the gear and about 3k per food item.