Boss Boat AM FM AUX USB Bluetooth Radio&6 Black Marine Speakers, 400W Amplifier By admin in boss November 19, 2023 In this case, the MR1308UAB. Front AUX (Auxiliary) In – This input on the MR1308UAB that says “AUX” is an interface that allows the input of audio signals for MP3 players, headphones and portable music players.