I found the newest BIOS (it's version 0100) here:
However, it still doesn't show up if you simply search for all downloads for DZ77BH-55K - someone should probably update this file so that it shows up in the search properly. Otherwise no one else will be aware that this update even exists.
I really appreciate the information provided. I reported the situation to the appropriate team in order to update the page.
Thanks and regards,