USB (Universal Serial Bus) connections send digital information to any device, while an AUX input sends analog signals. Now, this digital-to-digital transfer allows for better sound quality without any loss while converting the audio. But since the AUX transfer analog signals, the other device would have to convert it into digital signals for you to listen to the sound. This will lead to little distortion or loss of information. USB transfers data as you would to a computer, while AUX cables transmit audio as you would to an amplifier or headphones. So, you’ll notice a difference in audio output when you play from the two inputs simultaneously and USB definitely sounds better.