I did this before with a player piano. Used the audio out and put in a piano microphone inside the piano, ran both to a mixer and the output of the mixer into the sound system. I can play the piano and accompanied music, but can also be used for just the piano if someone is playing.

Was easier to hide because it was not acrylic. Agreed with other posts that unless the manufacturer has mics built in, there is no way to send the piano sound out.

used one of these mics

[Link: shure.com]