Why not use the even smaller speakers that you put in your ears, and then you can hear it. And it's inaudible to every other human. FWIW, both Spotify (Jam) an

Why not use the even smaller speakers that you put in your ears, and then you can hear it. And it's inaudible to every other human. FWIW, both Spotify (Jam) and Apple Music (SharePlay) have a feature to sync audio playback and give both participants the ability to control the music from their phone. It was probably targeted at CarPlay/shared speaker situations, but it works great for this.