I don’t see why the mxo2 mini would not work in that situation. I do something similar with mine to capture input from another machine.
Ensure you are capturing via hdmi and that you shut the mxo2 down and do a full reboot if you have issues. That seems to fix random yuv vs rgb interpretation issues. That said, the above syphon ought to work going from fcp to qc. have you tried it? I suspected you would want it for something like mapping. Seems appropriate. I think it should work in that light. Follow those instructions and apply the effect to a nested sequence.