Egidius,
Seriously, the guy sold you his ZH-270 and then wanted to buy it back?! I wonder what flipped him. I would never sell my ZH-270 unless I was absolutely sure I preferred the new amp. I'm the one who generated this thread and I've since bought a sold two more amps, but I still have the ZH-270. I'm afraid my next move is to compare the ZH-270 to the new Berning ZH-230. And with regards to Leben CS-600, skip the integrated Lebens and listen to the CS-660P. I haven't heard the ZH-230 yet, but at this time I've narrowed my upgrade path to one of these two.
As for Usblues's comment, ones tastes can become more refine over time. I think it sort of depends on what you listen to and what you listen for. My musical tastes go in cycles depending on the season, but my love is mainly for acoustic guitar and jazz piano, and the piano is a difficult sound to reproduce very accurately IMO.