Ixion is garbage even in burst team - it doesn't affect burst damage, only burst streak damage. If your Huanglong is LB0, Amaru is better in every situation. If it has 3-4 LB - when your assault lvl is very low, thay are almost the same, but the more assault you have - the less profit you get from character attack eydo, but elemental modifier gives the same profit- it is multiplied with character attack so i recommend to keep Amaru as main.