I come here to thank the forum for having helped me to succeed in recovering my MP4 player (bought on ebay).
But I would also like to help the ones who have the same player too and who are searching over there for the right firmware in order to make their player reborn.
So this is my player:

firmware: B806K1V2.0
core: 9.0.48
Of course, you will have to follow the
dead player recovery guide, you'll have to use the
MP3 utilities 4.09 and use the following firmware:
B806K1V2.0_2006-10-30_9.0.48
(this firmware has been found
HERE)
And like so, this player will reborn

with all the tools inside: video, music, FM, voice recorder, images browser...etc
I also advise you to check the
removing memory hack. With my "supposed 4GB" player, I used it and finished with 2 real Gbs, personnally that is still enought memory for me.
I hope that I helped some of you :? and sorry for my bad english.