Tascam GB-10. If you create the audio tracks as either MP3, 32-320kbps, 44.1kHz or WAV, 16/24 bit, 44.1kHz, they'll play. I have no problem with mine.
Edit to add: I use Audacity to adjust sample rates etc, and sometimes to adjust pitch at source so I can also use the track with Nux Mighty Plug or Boss Katana:Go.