HiFi external audio [e.g. digital piano] together with microphone use

I try to have HiFi audio from my digital piano together with speaking and singing through microphone in Zoom in W10 for music and singing teaching.

I attempted a USB mixer [with microphone + piano input]; but with the mixer as input in Zoom you get still distorted audio with the high notes. Even with original sound setting. So that’s not the good solution.

If you share e.g. YouTube sound in Zoom with Screen Share Audio Only, you get very good quality sound. That’s what I want to have.

So: I want to connect my digital piano via screen sharing and together use my microphone. Alike talking together with a YouTube movie.

How do I do that? I have searched everywhere, but nobody seems to understand.

Or can you please add an input selection in Zoom “Audio Settings” where you can select a different source (in this case my USB sound card) which is technically handled like Computer Sound sharing?

P.S. Teams and Skype also don’t provide high quality audio in this manner. So, be the first….