Hi. I just had solved my Build Library problem. Use my solution on your own risk.
The solution is the following:
1. open up a player (find 8 screws, not 6, 2 of them are on the left side of the player under the round stickers)
2. jently take off a circut board. (you need to access its bottom)
3. Find a memory chip. It is labeled like "samsung k9hbg08u1m"
4. find chip's key meaning start of pin numbering (small circle on the corner). There are 48pins. 24 on the left side (1-24) and 20 on the right (48-25) see chip's manual http://catalog.gaw.ru/index.php?page=document&id=11348 page 4
5. On the right side find pins 32-29 (find them as the second 4 pins from the chip's circle key opposite corner)
6. Connect them together with some metalic wire (don't touch two middle pins on the right side of chip, it is chip's power supply).
7. Holding those pins together connect USB cable to player's socket.
8. After a while player will show error on its screen, get metallic wire out of pins, and then the player will be available as flash storage on the PC.
9. Format flash storage with quick format.
10. Disconnect and assemble the player back.
11. Connect to PC and upload new music.
12. Feedback to fzymarev()yandex.ru