What exactly are the qualities you are looking for in a headphone, or the kind of music you listen to ?
Anyway, here is my short impressions of the K550:
For the present going price of $200, it has very good resolution and definition. I have not heard many but for those I heard the K550 is amongst the most detailed I heard at this price and certainly superior to the FA003.
The real strength of the K550 however is its soundstage, it was the best I heard in a closed phone. You can distinctively hear that it is closed, and it still lacks behind the open and airy feeling I heard with some open phones.
Well then, what's the deal, you may ask. The soundstage of the K550 is spacious, and along with that instruments are afforded better breath and the envelop of a muscial note is allowed to develop in a fuller manner. Plus, the positioning and definition of instruments within that soundstage is precise. From memory, as an open phone the K701 soundstage is even much more open and spacious but K550 has the upper hand in positioning.
I previously elaborate this in a Grado thread, a musical note can very roughly be thought of as comprising three parts : the initial attack, the main thrust, and the subsequent fade out. The Grado RS2i that I owned, at twice the price of the K550, do not allow the musical note to develop in full, but instead emphasize the initial attack, the subsequent fade out and decay is mitigated. Thereby giving an aggressive presentation.
In contrast, the K550 is amongst the best I heard at its price range in this regard. The muscial note is given a much fuller expression. The ebb and flow of the muscial event, the degradations and phrasing is easier to follow. The K550 is for those who appreicate subtlety, but I feel some system will not be sensitive or good enough to reveal this strength of the K550.
Granted, these qualities are less relevant for those "one note bass" and certain genre, and some will prefer the aggressive, exciting presentation of the Grado, which works very well with rock and certain genre, but ultimately that is a kind of coloration if the Grado fans will forgive me.
Now, there are lots of comments over the forum of how these phones sound thin without a good seal, and I can certainly appreciate where are they coming from. The funny thing is, I feel the designer of K550 just cannot turn out a thicker sounding phone but at the same time have the spacious sound of the K550...You see, by virtue that the instrumental images of the K550 is spaciously protraited within the soundstage (for a closed phone standard), it would be difficult to ascribe a thick and dense imaging at the same time. One cannot have the cake and eat it too. Ultimately you have to know your own preference and decide whether that is the kind of trade-off you are willing to take.
The real draw back for me with the K550 is tonality. I would describe it as dark and lacking in tonal colours. It is dark not in the sense of lacking treble extension, but an overall blackish tone with everything it plays. I am trying to describe the subtlety of sound here and a little lost with words, but those who have heard it may understand what I am saying. Somehow, AKG do not seem to have an history of not getting the tonality right. The K701 has been decribed as "plasticky" in its tonality. The K550 do not suffer from this, but neither does it excel. My brief encounter with K271/2 suggest that those phones may have better tonality than K550. That said, the drawbacks of the K550 in this regard is one of omission rather than commission, it certainly do better than the K701 in my books.
Another minor issue is the K550 has a slight tendency towards sounding clinical. Sometimes it does not have the bite and excitment when called for. I would not make this too big but they are not for rockers. They need a little time to run-in and everything just get better overtime.
