If anybody interested, I got luxman 509z last week. I traded 507z towards it. The 507z is already build like a tank, but to me the 509z build is another level up. The speaker terminals, top cover , side panels - better quality. But what surprised me the volume knob and input selector knobs are also on a different level- smother and more precise.
i got mine brand new and now it has about 30 hours on it, I already can say that it’s even more naturally sounding with even blacker backgrounds than 507z. My personal opinion - when burned for 300-400 it will exceed 507z on all levels.
With every solid state integrated I personally owned (pass int-250, gryphon 300, plinius hiato, accuphase E-800, gamut 150, luxman 509x, luxman 590axii, mark levinson 580.5) i always herd some hardness at the beginning. With 509z - not a case. This 509z is a real gem. Granted I learned a lot for the last few years about system synergy, cables, isolation - so it’s all contributing to the sound.
I am just a customer and not affiliated with luxman in anyway.