The 1.8V adapter arrived yesterday and I was able to successfully flash the chip. I used flashrom on linux for that.
It will detect the chip as:
Found Macronix flash chip "MX25U6435E/F" (8192 kB, SPI).
I found the reason why the modified bios failed. I'm using AMIBCP v5.01.0014 to modify some bios options and it seams that this version destroys something in the image. Now I will try to modify the options by hand to see if that works out.
And I modded the motherboard a little bit for easier flashing ;)
I tried to just remove the asrock protection and then flash the bios. Same problem ... The machine won't boot. Does someone have an idea what could go wrong ? Signature check maybe ?!