Boss Audio MGR300B Marine Stereo w/AM/FM/BT/USBMGR300B Marine Stereo with AM FM BT USB The MGR300B stereo packs a lot of features into a compact round, gauge style design that fits into a standard gauge opening. Crank up some AM FM radio, or plug a compatible device into the rear USB Aux input. The large backlit LED display lets you see what you're hearing with just a glance, while the IPX6 rated water resistant face panel and big, easy to use controls are made to resist sun, salt, and moisture.