Be sure the cable is good. A bad cable connection will sometimes give you a transistor radio quality sound. Swap out the cords.

Bose gear usually sounds good, and so does the piano so there's something going on with the signal chain. If you have a direct box impedance matcher.... try that too.

I know it sounds obvious, but be sure the EQ and the input levels are properly set.

Try running some other thing, such as an MP3 player into the Bose using the same cords.

It's a game of detective.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.