There are plenty of people on this forum who have and like the HP-3’s. Here’s our thread. Unless you can get a great deal on the Klipsch amp, I don’t think it should be your first choice (but I haven’t heard it so I could be wrong). Although since you live in Japan, it’s difficult to give reasonably priced recommendations. I did some searching on the Amazon.co.jp and a lot stuff we’d recommend isn’t there. The RNHP is there, albeit somewhat overpriced.
Also you are aware of just how different the HP-3 and HD800S sound right? The HD800 is bright and analytical while the HP3 is warm and laid-back
Edit.
What have you owned previously and what are looking for in sound now?