How are the K501? Haven't really heard about them recently so I'm curious about people's long term impressions.
I've owned these since 2001. I love them and will never sell them. They have no bass, they drop off a cliff at like 100hz so what you do hear is upper harmonics of the bass that should be there, your ear kinda fills in the rest for you, a psychoacoustic phenomena. What this does do though, is leaves rooms for wonderful mids, smooth highs and a pretty decent soundstage. THis is probably another effect where your mind has no bass to concern itself with so the attention is free for the rest of the frequencies.
They require an open mind but they are far and away the least fatiguing headphone I've ever owned. Technically flawed but they have their place in my lineup.