Your computer sees the entire mixer as a single input device. But you will not be able to hear anything with the guitar on 2 because the 1/4” input is a line input not an instrument input. You will have to use a preamp.
I did a weekend hack to build a web interface for the Spleeter. I think it works fine for now to separate vocals and instruments. You can try it out here:
I did the bass backing track generator as well. It's there on your profile page when you're logged in.
Basically, it uses the same tool under the hood. I would like to get feedback on it. For ...