an old trick was to burn the files into an audio CD and then rip the audio CD into the format of your choice - don't know if you can still do this as I haven't kept up with it
for the future I would recommend trying to stay away from purchasing products that force you to use products of the same brand...
iTunes is "free" -> cheap/easy songs from iTunes -> songs don't play nice with other players (digital and physical) -> need to keep using iTunes/iPod...BARF