Accuphase voltage conversion

I assume you must replace transformer. "Authorized" dealers will charge arm/leg for it.

There are certain logical ways to examine which unused taps should replace ones already currently connected. 
Often on PCB you can spot the input AC voltage printed than measure voltage accross the unused taps so it's the desirable one to be connected.
For safety I'd disconnect power transformer and run tests with 220V than run tests with 110V so to find matching unused taps. The color code on output taps of power transformer can often give you some tips, but to be sure measurements can give you precise picture of your project.

Bear in mind that local Accuphase distributor won’t be very happy knowing that you have Japanese unit. By their terms it’s "Unauthorized" and they will simply refuse to provide service.
Contact Japanese service provider preferably via Japanese website.
Tell you’ve moved to USA using Japanese and not English.
The other simpler way is to wire 240V dedicated line out of the distribution box. Thus no internal mods needed.

George, 
What is difference between qualified tech and unqualified? Is there licensing for working with electronics? I doubt it. You get lisence of electrician, but for electronics repair you don't  need even that. As to safety, there's plenty of information on how not to get zapped.

hmmm... 
I started changing tubes in my mono console system when I was 8. Than started repairing TV not too long after.
Never bothered getting lisence of electronic tech and still prefer to repair my own electronics as a matter of fact without help of lisenced tech.
License is probably something to do more with money not with actual skill or trust. 
Number of possible connection dictates to use logic to identify the right terminals more than knowledge of electronics or electro-magnetics. It means that there are color codes to ID either by measurements or by asking crowd or by asking manufacturer directly in Japan who will most-probably share this information. 
As DIY tech I've been able to receive or download lots of circuit diagrams that carry bunch of usefull information about voltage across certain terminals and wire colors. It might be harder to get diagrams for later models, but if available for earlier models the color code can very possibly match the newer model.