This is a pretty interesting piece. From a distance, it’s a 4-in, 4-out USB 2.0 recording interface, but its monitor mixer application includes most of a real mixing console (minus the physical knobs and buttons, of course) built around the PreSonus StudioLive 16.0.2 mixer. It offers a lot of flexibility in building studio headphone mixes, and you can even mix a live show with it. Visit the Reviews page, or just have at it directly from here. It addresses some test procedures, which might be interesting reading even if you don’t need another interface. 30 pages of PDF, so you’d best download it and read it at your leisure.