My mixer (DJM-900NXS2) has a bunch of outputs. I'd love to be able to use them all!
For example, I have one output that's just the post-fader A channel, another that's the post-fader B, another that's the mic… I'd love A to just affect one layer, and B another. And if I could use audio in from the mic to temporarily show my video - that would be amazing.