I also owned a pair of the 595's about a 2 years ago.
They did sound sort of bass shy and were lively, forward, and extended, and sort of easy to overdrive.
One of the drivers started rattling about 10 months ago, so I sent them, under warranty, to Sennheiser and they sent me a new replacement pair.
The replacement pair sounded VERY different!
They are the ones I descibed on this forum as bass heavy, sort of boomy, and rolled of on top. I prefered the sound of my first pair, but I can drive my latest ones to louder volumes without break-up! These newest ones also seem less efficient than my first ones as well. This last pair doesn't really sound bad at all, it just doesn't have the clarity and liveliness of my first pair.
I noticed the differences soon as I put them on for the first time.
I thought it might have been a burn-in issue, but it was not.
Its definitely not different tastes or perceptions, its real!
Maybe the impedance WAS different, I cannot remember what the impedance was on my first pair. They may well have been 120 ohms. Does seem sort of like their box may indeed have said 120 ohms. The first pair were made in Ireland according to the box that came with them at the time.
I went and dug out the original box for my latest pair, that I still have on hand.This latest pair is 50 ohms, and they 'Designed and engineered in Germany- acoustics made in europe-made in China', according to the original box.
Has anyone ever compared the sounds of the 50 ohm and 120 ohm versions?