Sucks it broke but at those power levels it's somewhat inevitable. I wonder if a single turbo setup would actually be more reliable than RB turbos despite making 100-200hp more due to the reduced exhaust back pressure?
On the damage it looks like typical N54 knock damage to me. Perhaps it was tuned a bit too aggressively or you just got unlucky on meth flow or fuel octane for a moment. It only takes a moment to blow up.
Mike