I've got a pair of the original stax sr-lambda cans. and they are wonderful. I prefer them to the koss. but then again, the koss is still in production, with warranty.
I love my stax. The midrange is so full and lush. but they are really a mirror to your source. if any part of your system is weak, it gets revealed with the stax. The excel with classical and acoustic type recordings. but I do enjoy a bit of prince every now and then. The bass is full and deep, but does lack a bit of the "slam" you get from a dynamic can. the highest end stax are said to not have this problem.
as far as being expensive, i got my set for 300 bucks, which included the "energizer" that you hook up to a speaker amp. Nothing I've heard can match this package at this price. bang for your buck if I may. stellar.