I get a odd harshness in the upper midrange and lower treble out of my MA900 on my system, I have to switch tubes to fix the problem with the MA900 while my K612 is a bit harsh on the tubes the MA900 likes. I guess it shows how greatly different systems can affect headphones. It's likely the K612 not having good synergy with your setup. AKGs have always been a bit of a pain to find the right synergy for in my experience.
Edited by kman1211 - 12/4/13 at 7:19am