Can't get P104/P106 to work with other discrete GPUs (AMD/Nvidia)

[unkelsunk]

I own two P104-100 and one P106-100 and all cards are working. I have tried and gotten them to work with my Intel i7 6700 iGPU (HD 530) but I can't get any discrete GPUs to work in combination with P104-100/P106-100.

Cards I have tried with so far, AMD Radeon HD 7450, AMD Radeon RX 570, Nvidia Quadro P1000. I get screen output from all setups but all rendering is done on the card connected to the monitor. The mining cards are chosen in Nvidia Control Panel but it doesn't seem to help.

The reason behind this is that I want to use the mining cards in my server, which doesn't have Intel iGPU. I have made a lot of progress getting P104-100 working with vgpu_unlock but since there is no NVENC onboard, I need another card to do the video encoding.