Q: Does the MENTOR support MP3 files?
A: No, currently the MENTOR does not support MP3 files or audiobooks.
So apparently I have mistaken this ereader for Astak's EZ Reader Pocket Pro, which does support audio files. And this Mentor probably has the audio jack just because the manufacturer included it, but their Astak firmware doesn't support it. I don't know why.
Now I don't know if I'll keep this or not. After all, I could still listen to my audio files on my iPod instead, and it would be more convenient since I wouldn't need a special connector for my headphones. I could still keep my folders.
But then again, there's that WiFi Nook...