I managed to make the boot sequence halt using the Esc key, but I got no image, well there was one! grey line in the top of the screen and the monitor reported running at 31.7 kHz, I did this before knowing the space bar thing, I wonder whether pressing space will help there?
EDIT: I am way too much of a noob to try making my own kick-roms... I wouldn't even know where to start on that one

EDIT2: I now managed to get the early boot menu

Now I try figuring out what ID my SCSI CD-ROM drive has... there are 4 jumpers : : : : and no. 2 is closed ( : I : : ) I figured that would make it SCSI unit 1 or 2 but no dice when I set it up like that in the CSPPC menu... at least if I only have to do stuff in the SCSI menu, I honestly don't know