thl, currently most nano-clones do not support file browsing, only folder browsing. The recent thread by Rolleyflex at
http://www.mympxplayer.org/viewtopic.php?t=1485 talks about merging various firmwares to enable the file browsing function. It may or may not work for you. But take note that by merging wrong firmwares together, you not only risk killing your player, you might even render your player totally dead unable to recover.
Good luck.