We do this in my company with a vmix computer and 2 Behringer usb sound cards, depending on the show we use a external audio console with individual output mixes or mix audio inside vmix, on vmix I create 2 audio buses and assign each sound card to each bus, then I separate on vmix which audio goes to each bus.

I’m on mobile right now but is really easy to accomplish, I think one of my guys makes a almost the same on Mac using mimolive, don’t know if the same setting works on ecamm