Sorry to wrench up your works 😉
I use the Presonus 1818 interface. In my setup, I have 18 channels of input, and 18 channels of output. I am only using 8 in, and 8 out at the moment. The 8 ins are my built in mic pre's on the front of my interface, and the 8 outs are a series of TRS jacks on the back. These outputs are known as your hardware outs. They can be used a number of different ways. For mine, outs 1 & 2 are the mains which go straight to my monitors. Outs 3 & 4 are vacant at the moment, but could be used for another set of monitors to A/B between. Outs 5 & 6 got to my patchbay, which I use to send a signal to my outboard gear(I use this for re-amping a lot as I have a hardware re-amping box) Outs 7 & 8 are my headphone outs. I can switch the outputs of my busses in my DAW to any of these hardware outs I choose. I usually have my Master/Mixbus/Twobus outputting to 1 & 2, then I output the reference bus to 3 & 4, so I can bypass any Master bus processing and listen to the reference clean to compare it to my mix. This method makes level matching a snap because all you have to do is move a fader.
Like most things in mixing, there are several ways to accomplish the same thing. Hope this adds fuel to the fire 🙂