http://www.mp3-box.org/mp3-boombox-usb/
Mass wma to mp3 converter?
i have 400+ songs in wma and i want to convert to mp3 in one click and let it go. is there a program that can do that? because all the programs i know i have to click one by one… i want to put the songs on a USB flashdrive so my boombox can play 
dBpoweramp or Foobar2000
But if you do that conversion, all your 400+ songs will lose sound quality because you’re converting from one lossy format to another. To avoid that, you’re better off re-ripping all your CD’s to mp3 format, granted it would be a hassle. Or if you re-rip to a lossless format you’d never have to re-rip again, you could convert to any format and bitrate you want at any time.
J30RED PORTABLE AM FM CD MP3 USB SD AUX INPUT BOOMBOX RADIO