this enermax should be enough, but if you use specific rails you may have issues like the one you got.
a) try to disable physx in nvidia drivers (set cpu)
b)use different 12v cables (8pin/6pin) in order to use different rails
Based on the specificationt table, your psu has 6 rails, use one rail for each connector per card (8pin will be on different rail than the 6pin).
Each card has 1x 8pin and 1x 6pin connectors, that way you will use 4 different rails out of 6. If its a rail problem, it should be fixed that way