I have been looking at something in Japan too. Unfortunately, the 15% tariff bumps up the price too much. You might want to look for something used here on Audiogon, or check the consolidator www.hifishark.com. Here is the link for the 507Z. https://www.hifishark.com/search?q=luxman+507z
My opinion is the Luxman products are generally quite good. I personally prefer the Pass Labs products. I doubt if you would be disappointed by either brand.
Here is another option: I upgraded my pre-amp last year to the LTA MicroZOTL and love it. They have a nice integrated too. https://www.lineartubeaudio.com/products/z40-integrated-amplifier
Lots of choices. Have Fun.