Jack, I think that is what confused me and prompted me to ask the question. Say I have a line input (from my keyboard), and a microphone input, both coming from my audio interface. In my DAW (windows), those choices show up on a pop up to select the input for a given track. So when you say "doesn't have an input mixer", do you mean that you are not able to select a particular input from the audio interface? Or do you mean you can't mix from multiple sources.
Thanks for your help with this.