Just saw ndburley's post. Exactly my opinion. For Bob Marley, Fleetwood Mac, and real heavy bass music like Gorgon City these are perfect.
All our ear shapes are so different and our likes and dislikes so different that all of the following is only IMHO.
I now have used the Havi B3 Pro 1 Dual Driver for a while, as well as the Vsonic Vsd3s. None of these give anything like the bass of the 550'sx so I much prefer the 550'sx for Bob Marley etc. and they do need equalising more than any other earphone I have had.
Nevertheless the Havi and the Vsonic are by far the better earphones. In fact they may be the best earphones for the money as they are superb with jazz, classical and pop, guitar, folk music etc. Neither are 'purrfect', but not too far away. They are more similar than different, but picking hairs the Vsonics are slightly smoother but the Havis are slightly more accurate in the highs and a little more articulate. The Havi Pro's have the widest soundstage I have heard and the Vsonics have one of the deepest soundstages I have heard. Strange but true. I am happy with both, amazing value, and enjoy them equally. The Havis are much harder to drive though, but fare well with my Fiio X1 (quite brilliant), but not with my old Samsung S3 or Sony Z3.... too quiet for me. The Vsonics are much easier to drive, so if you want them for a mobile phone or bog standard MP3 player they are better by far. For headphone amplifiers the Havi Pros are probably better. I would say at their price range of £30-40 they are both 10 out of 10. I am not going into detail because I am just trying to put them in perspective against the sx'550, which are worth listening to in their own right.
So the Project Extreme sx'550's will be a 'basshead's' dream and worth having in a collection to cover all music types. The Havi's and the Vsonic's are just excellent and reproduce highs and mids exceptionally well. Although many have reacted to the marketing of the sx'550s they are a 'real' earphone and should be taken seriously.