From the Owners Audio Handbook, which you should have been given with the Trophy :
Specifications :
USB port with flash drive and MP3 player support
(file types supported: AAC, FLAC, MP3, OGG, WAV and WMA)
You also need to make sure that none of the file ( Track ) names exceed 59 characters in length -
The audio system doesn't like it if they do ( although it doesn't tell you this little gem in the Audio Handbook