how do you setup multiple gpus for rendering?

I’m trying to use 2 gtx cards (980 and 1060) for gpu 3d rendering (octane / redshift / cycles) and I’m having issues. I can see both cards in nvidia-settings panel but none of the renderes detects both. They see only the one to which monitors are connected to (in my initial test - 1060). All suggestions how to make it work are greatly appreciated.