As you have found out already It's not a adfu device, It's a Rockchip.
and Mp3 Utilities doesn't work for Rockchips.
Do you already have the right firmware?, if not you need to find a working firmware for your player.
PLEASE try the SOFT Dead player recovery procedure below, it could save you a lot of hassle opening up your player:-
All you do is this,
1) Switch the player OFF using the main on/off switch.
2) Hold down the "MENU" or the "PLAY" button and keep it held down.(try the other buttons if these dont work)
3) Connect the usb to the player.
4) Wait for about 10 seconds before releasing the menu key.
5) You are now in "RockUSB" upgrade mode!
6) Then just Start ConsumerUpdate and upload a working firmware and try it!
ConsumerUpdate should also REBOOT the player before starting the upgrade.
MP4 Nation Forums • View topic - LINKS TO VX858LE CLONE FIRMWARE