Update: I discovered that while the product's model name is EBK001-DZTEP-V5, it says "Explay TXT.Book" in the Info dialog, and judging by the form factor it should be a TXT.Book.B63. Does anybody have the same model and perhaps more info?
I finally found out how to enter the upgrade mode: keeping the power and menu button pressed and connecting the usb cable shows it as a Samsung CPU device.
It looks like Orsio's firmware can be put on it, but the only place where people seems to try these things is
www.the-ebook.org, and Google Translate shows its limits...