Routing usb for livestream

Anyone know How to route mixer stereo usb out channel 1 and 2 to OBS software on Mac while using mixer xlr input channels and usb backing tracks input via usb as well. Hope that makes some kind of sense. Anyone?

There’s this video that’s pretty comprehensive. Not sure it covers what you want but, if all else fails, contact the author - https://www.youtube.com/watch?v=YJVuOo6KNtM