Garageband and Yamaha Clavinova CLP-685 Recording

Hi,

My daughter plays a Clavinova CLP-685.
We want to connect it to the Garageband App on the MacBook.
So far so good, we made it allowing her to record what ever she plays on the piano.
But..now next step. She want to record different voices / instruments using the CLP as a keyboard, in the same time using the CLP Audio-In for playing the result onto the built-in speakers of the CLP. In other words, how can we switch the keyboard in the CLP silent at same time playing AUX in-sound? Turning down the volume of the CLP will not work as it also affects the audio in.
We want to use the keyboard as MIDI-in for the Garageband and the CLP speakers as audio out of such at same time.

Kind regards