I have an all X problem which I'm assuming is power related.
At first it was hashing away nicely for about 8 hours... then it stopped. After restarting, and then doing a full factory reset.... it will only run for about 1 hr before stopping.
power supply is a new Corsair CX750M with nothing else plugged in. Before I ran the cube on it... it was powering a 49 port USB erupter setup with no issues. :/
I will bet your all xs problem is due to one flaky board.
Try running one board alone and then add back one by one to identify the offending board.