CameR's colleagues probably were about an additional device that you can find on the familiar auction site under the name "mp3 changer". Only the plug fits the model and plugs instead of the factory changer. Sometimes it is possible to connect in addition to the factory changer, but you need to verify it before buying. Depending on the model, it has a USB, SD, mini jack and Bluetooth socket. Big choice. As for the factory solutions, unfortunately RCD 300 does not support USB.