We use vmix also with hardware mixers as a graphics generator. We would like to use key of the hardware mixer and thats why would like to rise the black level of vmix footage. I have not found how to rise the black level of the vmix input so that blacks would be more gray (we will key away the totally black part of the picture). You can do blacks more deeper but not whiter? Well one way is to rise all rgb sliders but that also has effect to whites (they will burn).

I believe others also use vmix as graphics generator for hardware mixers - how have you resolved this key issue?