Update: Problem solved ! 

Here is what you should;
Go to BIOS and update the bios to 1.D version
then go to Settings>Advanced>PCI subsystem Setting
Above 4G Decoding set to Enabled
(thanks to Tummler for settings)

And very important thing:
U should use Skylake CPUs
If you use Kabylake u can mine only with 4 GPUs
I was in trouble because of that.

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I have same Z170A Gaming M5 Motherboard and Kabylake CPU G4560.
6 GPU works just fine on Windows10, but no more than 4 GPUs on Simplemining.
So, do you think that Kabylake CPU has limit only on Ubuntu (and not on Windows)?