Those are great cards you should be getting 850 min from each one. Here are the settings I use:

I 20
g 1
w 512
thread-concurrency 32765
gpu-engine 1000
gpu-mem 1250
gpu-powertune 30
gpu-fan 100

You are getting hardware errors because your thread concurrency is too low.

Try this and let me know if it helped. If not I can help you more.

If I helped please send some LTC my way

LXSFqWQ6r5gAYXw3ZtxvFjS3iUBQsTeBah