Xerxes = Arta-Xerxes


I also concluded that Xerxes and Arta-Xerxes were the same king. See

In my model, Darius the Mede (Darius I) and Cyrus the Persian (Cyrus II) become kings in Medeo-Persia at about the same time, however Cyrus II outlives Darius, perhaps by about six years as you propose.