[johnnym]

I did try bypassing the POST, but it didn't pay attention to me, or I didn't do it right (Pause/Break is equivalent to Stop on PS/2 keyboards, right?)

I think so. Say, what's used as power-on key on a PS/2 keyboard then?

Wow that machine is reluctant to cooperate.

Does Stop + N work to reset the NVRAM settings when the NVRAM is inserted? The manual says you have to hold these keys until the banner appears.

And maybe best to continue that debugging with non-essential hardware removed or disiconnected. The machine needs a minimum of four identical memory modules in the four slots closest to the CPU slots and for the glass console a graphics card. i'd remove anything else (maybe also remove power from the drives) just to see if that makes any difference.