It seems I'm out of ammo. The log I got was limited to whatever I booted on.
Meaning it's a log about the live session, not about the prior failed boot
from disk.
Also, the vga rom option seems to be useless, since SeaBIOS is already
displayed.
I'll see what else I can try for the 6 cores.
But else, tomorrow I'll try a 4 cores rom, with microcode updates and
SeaBIOS.
I can access my drives from the live session btw, but the big drives made
mouse and keyboard unresponsive, even after unplugging/replugging.