According to the manual you can play files on an iPod or a USB memory device. It says nothing about other MP3 players.
It also says it can only read FAT16 and FAT32 formatted devices, and can only play MP3 and WMA files.
Further:
"Only music files that are not copyright-protected can be played on
this set.
Contents downloaded from pay sites on the Internet are copyright
protected. Also, files encoded in WMA format when ripped from a
CD, etc., on a computer may be copyright protected, depending on
the computer’s setting"