They are my first full size cans, and I had been leaning towards the m50s, but that would have meant stretching my budget considerably. I have long been a koss fan, my trusty ksc75s are still going strong after 10 years. I picked up my set for $39 on amazon, and what a bargain they are.
I immediately ordered m50 pads and although I enjoyed the enhanced detail, soundstage and improved a comfort, I felt that some of the warmth that was apparent with stock pads had been lost. I started playing around with taping over the outer holes in the cups to see if this would reduce the somewhat fatigue highs that were now present and to bring back some of the bottom end.
Covering although the holes muddied the sound a lot and the bass response was wy to present. I eventually found that covering every second hole was perfect.
I am continually amazed by these headphones and they adapt well to a range of musical styles. My next step will be adding a dac/amp to the setup to see how well they can really perform.