I listen to folk music gathered from the appropriate regions whenever I can find them.(And afford them) I highly recommend Yair Dalal's "One" album for Qarthadast and Saba, lots of atmospheric Semitic campaign tunes and plenty of tension and mobilization pieces for the battle map.
For the "Eastern" factions like Pahlavi and Pontos The Kamkars work pretty well. Those Persian drums are stellar in the battle map.