the mx550 are very good earphones , if you can get them stuck in your ear canal ( that is , you have quite big ear canals ) they're able to mime very nicely the hd650 sound signature , not joking ( use the search button , mx550 and my name to find related threads there are other very positive opinions on these buds )
Having got them more then 1 year ago , after mx500 and Sharp md33 and Westone Um2 , and px100 .. and others .. I still consider them unbelieveble value , this if you can use them fully inserted and covering the whole ear canal window perimeter ( to get near a seal for them ) .
Hope that helps.