Black screen on Mac OS 10.3.6 - Mac Pro 6.1 - Mantiz Venus - 1080ti  

Hey Guys, i am new here I just installed a purge-wrangler. First of all, I am not able to boot to system with EGPU connected. When I connect EGPU on login screen the gpu works in Cinema 4D (Octane render) for example. But I am not able to see the graphic card in system prefernces and when I connect screen - HP Z43 I have just a black screen. Any help with booting, or at least display connection to get it work ? 

My setup is Mac OS 10.13.6 on Mac Pro 6.1 with 2x D500 Fire Pro. EGPU Mantiz Venus v2 with Nvidia 1080ti. 

Thanks in advance. 

Lukas.