It's truly bizzarre. No matter what I set in the BIOS (ignore all errors, all but keyboard, USB keyboard by OS/BIOS, whatever), if I have the mac keyboard plugged in (directly, to the KVM, to the screen plugged into the KVM) the IP35 craps out just after CPU detection and just sits there wanting me to press Del but not recognising any input. The only way I can get the damn thing to post is to plug in a PS2 keyboard (wohoo, it's back to the 20th century) or to switch the KVM to one of the other machines, power on, let if finish POST/BOOT and then switch back.
Installing latest BIOS, made no difference