I offer no guidance on Accuphase in any way, but I can share some real-world import/export experience of electronic devices, Japan and how niche manufacturers tend to operate.
First, the boilerplate on the Accuphase website is just that. It is intended to discourage people from going outside of the "authorized" supply channel to protect the revenue stream of the folks that have to deal with the quirks of a different marketplace. In the case of Japanese electrical standards, you will generally find that most (but not all) are going to be compatible with 100-240 VAC 50/60 Hz. Some will have a physical switch on the device to adapt one way or another. Japanese home standard is 100 VAC 50/60 Hz. They do this because it's comparatively inexpensive to manufacture power supplies that can span that frequency range (required in Japan by regulation) and it makes adapting for international markets less costly (think the key export market of Australia). You may find there are different wattage ratings for different voltage and frequency combinations on a particular unit. The best way to determine if any given device will function without risk of damage in an environment is to look at the rear panel and the required-by-law voltage/frequency statement above the IEC power connection.
Second, you are going to Japan more than a year down the road. The Japanese home market can change must faster than ours as they often develop home market goods first and then trial them in limited export to see if an "improvement" really is what they think it is. This approach is supported by their incredibly flexible supply chain. It is largely based on what the US terms (and rightfully so) "cottage industry." You are best served by planning nothing one way or another until a couple of months before you leave.
Third, Japanese businesspeople tend to be conservative in.toeing manufacturer guidelines and very sticky about even thinking of bending those rules. Nobody wants to create headaches that can readily be avoided just by saying "no." Understand too that the Japanese language has no really direct equivalent to our English "no." There may be approximate equivalents to "F you and the horse you rode in on" or other negative responses, but none of them translate well and polite (and Japan is nothing if not polite) people would never say such things to a visitor. That all combines to mean you could get a lot of equivocation and no hard answers about a proposed purchase. If so, the answer they are giving you is "no."
Next, other folks have mentioned post-sale grey market warranty support and shipping issues. Those are both very real concerns depending on how tightly spares are controlled and how you're considering transit. I have seen Japanese manufacturers flatly refuse to supply spare parts for the repair of any device that did not go through channels, despite in-country laws preventing just that sort of stunt. That might be illegal but what can YOU, a private individual, realistically do about it? The components are probably available by the gross in Akhiabara (a Tokyo district) for a reasonable amount of yen. Getting them from there to here isn't likely. Shipping is realistically a bigger issue. Getting something like an Accuphase integrated or whatever back to the US will be complicated, expensive and annoying to an exceptional level under the prevailing trade conditions. And you really don't want to think about bringing something like that back via passenger air service. You will spend a significant chunk of time in CBP discussions on arrival at JFK or wherever listening to how much duty you have to pay and why. Worse, the dollar is not faring all that well against the yen and that situation is not likely to improve by next year. Capital One may not charge a foreign currency transaction fee, but if the dollar is so weak you're paying a premium, the thrill of a "from the source" purchase can be diminished.
Finally, I can tell you I've obtained some very unique and treasured things traveling in Japan, Taiwan, Germany, Denmark and UK on many occasions from the early 80's through 2013. I never had any sort of problem then, but the world today is not the same. You will have to decide for yourself and remember caveat emptor.