Hello All.
I was able to get 6 x RX-500 series running on windows 10 x64. After two days the stupidest thing I tried worked  .
1. use DDU to clean the PC from any previous drivers.
2. Disable 4G decoding so you can log into windows (only  for Z170,H170, etc.)
3. Extract older driver for RX 400 series in Drive C: (I use 16.9.2 )
4. Extract driver for RX 500 series in Drive C: (I use 17.4.3)
5. Copy and replace all content from "C:\AMD\Non-WHQL-Win10-64Bit-Radeon-Software-Crimson-16.9.2-Sep21\Packages\Drivers\Display\WT6A_INF\B307117"  to "C:\AMD\WHQL-Win7-64Bit-Radeon-Software-Crimson-ReLive-17.4.3-Apr17\Packages\Drivers\Display\W76A_INF\B313057" (Basically you copy the old driver over the new)
6. Install the VGA cards manually from Device manager in Windows pointing path to the new driver 17.4.3 in this case.
7. Reboot and enable 4G Decoding in Bios
8. Enjoy if it works for you.

You can try with different driver versions if they work for you. I`m happy whit the 16.9.2 for the moment but any driver that works whit 6 and more RX 400 series GPUs should work  .

I know  that this solution sound stupid but it`s tested on 8 different rigs whit Asus Prime Z270-P and H270 Motherboards and works like a charm.
I`m pretty sure only handful of files need to be replaced but I don have the time to test more elegant solution.

Sorry for my English and grammar.