Been using the Sennheiser HD598Cs + FiiO E10 for about a month now - consistently 2-3 hours/day, maximum of 7 hrs/day, varying from electronic or classical music to recorded school lectures and videos. The FiiO is probably not necessary considering the low impedance of the the HD598Cs (23U) in combination with output from a Macbook Pro, but should be noted.
Overall these headphones are very accurate, in my opinion, to what the recorded sound was intended to sound like. The sound is crisp, sharp, fast. Full disclosure, these are my first high(er) end headphones so keep that in mind. That being said, I really enjoy the sound and the overall comfort. At first I found them to be a bit finicky in terms of position on my head creating equal sounds in both ears. However, I've gotten used to how to adjust them to create equal sound bilaterally.
"But why did you by the closed-back version of the ever-so-popular 598??"
I work from home most of the time, and my fiance recently had a shoulder surgery and has also been home. In order for me to get through the 8+ hours of boring-ass lectures, my headphones have to be silent for those in my immediate surrounding. From my fiance, "I can just barely hear your music" when I'm listening to music waaaaaaaaay louder than I should be.
In terms of comfort you really cant go wrong with the HD 598's, open or closed as I hear the ear cups are identical. Once these puppies are one, they melt into your skull and eventually you forget they are even there.
In summary, if you are considering a new pair of sub $150 closed-back headphones, I would highly suggest Sennheiser 598Cs. My god, get these cans and listen to Yo Yo Ma perform Bach on the cello. Take a second to think about how amazing it is to experience the emotion that is invoked when music created hundreds of years ago is performed today. Cheers, B