Pros: Transparency, soundstage, treble
Cons: Comfort, perfect seal
This is my first review so please be gentle!
When you first put on this closed headphone, you'll be stunned how wide the soundstage is. Compared to my open Sennheiser HD600, the soundstage is equivalent! (though the HD600's soundstage is slightly deeper).
The K550 also trumps the HD600 in so many aspects including transparency, clarity and dynamics. On the other hand, the HD600 trumps in bass slam and comfort.
There is plenty of bass in the K550, but it's not as textured as the HD600 and as for comfort, the cups are really comfortable but the headband requires more padding.
The amp I used to to compare the HD600 and K550 was an Aune T1 with 6922 tube. I've only just upgraded the tube to a 6H23N-EB and the K550 sounds even better, but unfortunately I don't have the HD600 handy right now to compare on this new tube.
The value of this headphone is unmatched given how good it sounds and is possibly the best sounding closed headphone that is still in production. It's currently my favourite headphone for music, and in case you were wondering, this is my headphone preference:
AD700 < M50 < FA-003 < DT770Pro LE < HD650 < HD600 < K550 baby!