McIntosh US 110vac - good for Japan 100vac?

You are asking many different questions.

"anyone knows if i can use McIntosh power amp/preamp/integrated bought in US (110vac) in Japan - 100 vac" I think you should ask McIntosh this.

"can McIntosh convert or it has some jumper/swich inside to change to 100 vac" I had my MC275 serviced at my US Mc dealer who opened it up and changed some jumpers to make it a 220V unit, so this might be the case with most/all McIntosh units. By the way, McIntosh was telling me this could not be done!

" is McIntosh will still service US unit in Japan?" Again, you should ask McIntosh, and/or the Japanese authorized dealer. I would think so.

Then about speakers and amps, do some search here in the forums. For B&W 801 you will want a large solid state amp, probably a McIntosh MC402 as a minimum. McIntosh & B&W are generally liked together.

Thanks for response and suggestions.
I asked Mc service and they told me that once i move Mc bought in US to Japan - no service/voltage change over.

Looks like MA6900 - it is very easy to change to different AC voltage just by switching wires on main trans - so i am thinking too buy this one.

question - is it enough to drive Magnepans 3.6
(will keep b&w on accuphase)

seems like it is quite difficult to find McIntosh MA6900 used for sale...
they go very quick.