I think the K340s are one of the great headphones out their (mine are the same as philodox's) . That being said they take some modding, and some care has to be taken, as far as amping.
They take alot of power. Philodox is right in saying they take almost as much volume knob power on my amp as the K1000s.
Not the best example but with my stepped volume attuenuator. HD 650s the 2nd or 3ed. (7:00 O Clock) step huge volume and soundstage. K 340s almost 11:00 O Clock. K 1000s 1:00 O Clock then open the K 1000s wings 2 or 3 O clock all this at a meet in NY 2 weeks ago
not the best place but just an idea.
K 340 sound when propery amped. Sound stage is huge
the highs are as clean and effortless as headphones can get.
Mids are right where they should be very neutral, true to the CD and CDPer.
The bass is great surprissing at times because the mids are so well ballanced you might say these sound like they are a little bass shy then put something on with a nice bass line and wow.
Impact and dynamic is also suprising, eye blinking if you put in the right CD and turn it up just a little bit. Remember turn it up a click on the volume does little on such a power loving headphone as the K 340.
The ability of this headphone to pick up small details is also increadable.
Nice headphone. A little heavy, sweaty (hot in summer) and not as secure as say my HD 650. So no quick moves with these on.