I've tried to install both Promox 5.4 & 6.0 beta, as well as Debian 10 and each shows a blank/black screen after BIOS. The system has no integrated graphics, and I've tried 3 different GPUs without success (NVidia Quadro 580, ATI FirePro v3900, NVidia GTS 450). I've tried booting both via legacy and UEFI devices, enabling/disabling secure boot, changing the graphics mode between legacy and EFI without luck. Is there anything else I can try?