As you are using an Audiobox, you should already be aware that each input is mono.
Input 1 - Left
Input 2 - Right
Mono – one sound source, one location.
Stereo– two distinct sound sources, different location OR multiple sources in different location summed up to two audio recording signal (left and right). If the vocal performance is more than a single sound source; of course the nature of sound is not mono anymore; instead this is where you start treating them as stereo.
Audiobox USB Manual:
We recommend that you create a mono input for each of the inputs on your AudioBox USB. If you plan on recording in stereo, you should also create a stereo bus and assign it to the appropriate set of inputs. You can remove any bus by simply selecting it and clicking the Remove button. To customize the names of your buses, double-click on the default name to open a text box. When you have finished typing, hit Enter.