I have a board IS8XM (C226) from ThinkStation E32, I want to mode bios to add NVMe and E3 V4 cpu supporting on this board.

I download from [HTTPS]support.lenovo.com/ar/en/downloads/ds035753 extracted a IMAGEFB.ROM which is a 6.5M file, after mod this ROM file, I failed to flash to board because of CRC/safety check fail under DOS, and I can NOT flash it with version which support force flash as well.
Then I turn to SPI programmer.

The problem is, in this board, there have 3 spi chips(1M, 4M and 8M), I searched a lot did not find any hint which one and how I should flash to.
-- 1, what is the different of those 3 chips?
-- 2, the 6.5M file, looks like it is only able to flash to 8M chip, but from search result from internet, the 4M one also need to be flashed when you fix a board lost bios, it confused me.

anyone can share your idea? thanks alot.
the board's picture is here : [HTTPS] empowerlaptop.com/wp-content/uploads/2018/good/dmb10626-w1711-1.jpg

EDIT by Fernando: Thread title shortened and not required blank lines removed (for better readability)