Don't take this the wrong way, but I think you're not doing it right.

Your situation sounds like a typical DFU tools fix is needed. Remember to press the PLAY/PAUSE and M button (I'm talking about a regular M6 here) and keep them pressed until you have disconnected. It's a bit awkward, yes, but it really should work.
Prepare first: remember to put the files in the DFU Tools directory. Then, press the player's buttons and
keep them pressed. Connect it through USB.
Keep those buttons pressed. Start the DFU Tools...
while keeping those buttons pressed. Can't stress that enough.

Press the start button or whatever it's called, in the tool. Still have those buttons pressed, right?

It'll take a little bit before it's finished. Then, close the DFU Tools (buttons still pressed, of course). Pull the USB plug from your M6 and... finally let them buttons go! :D
Some have had to try this 10 or 20 times before it worked, but it'll work. First startup might give you a white or green screen (I had that) but it'll go away after a bit. Then you can start it and all will be fine.
Sorry about the 'buttons pressed' comments, but it's where most people have gone wrong. Just want you to bring your M6 back to life!

Good luck.