Taittiriya Brahmana i.2,6,7-Daivyo vai varna brahmanah assuryyo sudrah - Brahmin Varna came from Devatas and Sudra Varna from Asuras. Is this symbolic? What is the context of this verse?
Scriptures mention a lot of contradictory things, it has been a lot of years since they were written and for the same reason the statements of scriptures contradict themselves.
For example Taittiriya (7.1.1) says :
 was created, the Vairaja Saman, of men the Çudra, of cattle the horse. Therefore the two, the horse and the Çudra, are dependent on others. Therefore the Çudra is not fit for the sacrifice, for he was not created after any gods. Therefore they depend on their feet, for they were created from the feet.
Now this particular verse says that Shudras are not fit for sacrifice as they were created from feet of lord. Is that not contradictory ?
When reading scriptures in case of contradiction always consider the most logical statement legit. Follow Yoga vasishta who said-
The remark of a child is to be accepted, if it is in accordance with reason; but the remark of even Brahma Himself, the creator of the world is to be rejected like a piece of straw if it does not accord with reason.
To the above I would like to add that both Devtas and Asuras emanate from Narayana so Brahmans emanating from Devtas and Shhudras from Asuras is not something which creates discrimination source is still same and is one without a second.
Also it can be taken to be symbolic saying one who is Shudra by nature is more tilted towards Tamo-Guna and one Bramhan by nature is tilted towards Sato-Guna.