Is there a reason why I can't find a device that reads MP3 files off a USB memory stick and simply output an analog line out signal on RCA connectors. I'm not an audiophile, but I have a boombox that has a USB input, and many of the latest model cars are putting USB inputs as standard (eg. Toyota), so why isn't anyone making a dongle that could provide the same function so I can retrofit my existing stereo system. I understand power would be needed, but that's no big deal. Help?