PW2 Need help with writing image via Fastboot - "FAILED (remote: Invalid partition)" prob

Hi, I've got a bricked PW2.
I managed to connect it via serial port (Mac + Ft232R) and get it into Fastboot mode.

I'm using the following images: https://ixtab.tk/kindle-touch-images/PW2/

So far, I have successfully flashed only the diags_kernel.img. Here are the logs a) from the terminal:
b) from the serial monitor (using CoolTerm for Mac):
However, the other 2 images that should be flashed via Fastboot return the following error:
I've tried the images from PW section (non-PW2) - same story, only the Diags Kernel goes through.

I tend to think the memory of my device is corrupted or something. I have quite basic knowledge of Linux-based systems and would appreciate any help.
Kindly let me know if you have any ideas - I'll try them out and will revert with my findings.