Robert, you are awesome! I would very much appreciate if you took
some pictures. I did some more experiment today and had quite strange
results. Now that I understand that the two black and the brown wires
are the three phases and the blue is null, I hooked up brown with P1,
the two black ones with P2 and blue with null. When I plugged in,
I saw the power line controll lights 2 and 3 flash up real quick and 
then they were out. When I turned on the main power (T-switch) I could
measure 110 V at the auxiliary receptacles as it should be. However,
I could not find any 220 V at the round plug. I tried two variants:
with leaving protective ground open or closing it at N (I know,
this was only temporary ...) When I had protective GND on N I would
see the PL1 controll light flash tooo. But I never got any 220 V
between any of the pins on the round connector. Now this may be 
because I tried with the power unit from the VAX that has some
(unknown) power problems.

> The cable that connects the round
> connector to the `power & logic box' has only six wires, two from each
> phase.  There are a number of other connections available on the round
> connector, which leads me to believe it's a standard part for anumber of
> different power schemes.

From the inside it looks as if each lead goes to at least two of those
pins. This would seem reasonable as the pins themselves look pretty 
small for 800 W full power ...

> Here's the fun part!  Inside the `power & logic box', all three phases (
> no neutral!) follow a simple path thru a 20A 600V fuse, and then into a
> full-wave bridge rectifier, DEC part number 11-26520-01.  A couple of MOVs
> offer some protection from transients, and yet more filtering.
> 
> Now, the good news:
> 
> It should be possible to simply apply 220 volt single phase (common dryer
> power) to any two of the hot wires on the three phase plug!  No neutral is
> needed for the computer itself, altho any accessories plugged into the
> lower power-distribution box will need one.  These pose a small problem in
> that they are connected to different hots to more evenly balance the load
> on the three phase supply, but worst case they can be easily tied on to
> one phase inside the box-- best case don't use them!
> 
> I'll be making a cable to replace the factory assembly, and rewireing the
> distribution box to single phase, I believe.  It should be 100% reversable.

My plan is to buy a receptacle box for the original power plug and
wire that box near my extra circuit-breaker box in the laundry /
computer room in the basement. Given that the stange behavior of the 
power control lights are explained and my mistake in measuring the
round connector's voltage output is discovered, is there anything to 
rewire inside the AC power box?

I wonder, are we the first ones to fire up their 6000 in their private
dwellings? BTW: has anyone noticed major interference with radios or
TVs (the label on the machine talks about it ...)

regards
-Gunther