Ok so the only way to get amaunator as a faith option is morninglord.
Capstones require you to be pure 20 levels of x
This is from the release notes on lam what am I missing.
Favored Soul Angel of Vengeance:
NEW: The capstone has gained an Amaunator option:
Ascendancy: Bolt of the Sun:
Passive: You gain +2 Charisma and +2 to the Diplomacy and Spellcraft skills.
Active: You are able to cast the spell Sunbolt without using spell points.