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Not even that. i feel the 555s to have much more neutral mids. the m50s mids are recessed. Musicians playing in front of you just don't sound like that of the m50s. the highs are peaky and one-notetish too If I were to nitpick with the 555s, they might need more inner detail and a finer grained sound and maybe tighter and deeper bass but I wouldn't want them to have that tubby m50 bass wich is too much in the lower midbass region from 40 to 80 hz

I have to chime in for a sec.
 
Personally, I find the HD555 mids very tonally flat (as in "sharp" and "flat" like on a musicial instrument, so read flat here as "unnaturally boring").  Neutral? Hmm, nope.  I EQ my m50's like so...
 

 
...and I get a sound almost exactly the same as the HD555.
 
Yeah, the treble will sound tishy with the m50, but you'll get that effect with common consumer music on top-level audiophile headphones (i.e. HD650).
Now, I think of the HD555 as a mid-fi headphone disguised as a hi-fi headphone.  Notice that peak at 10 KHz.  That gives cymbals a nice, slow shimmer, but nothing truly realistic.  (That peak creates the HD555's surreal soundstage, though, by the way.)  The HD555 response does make most consumer stuff bearable, especially in the mids and treble, but bear in mind that it's coloring up the sound.  The frequencies are missing around 2, 4 and 8 KHz and above 11KHz, and that's usually where modern music has its overbearing treble.
 
Still, who's to argue?  This is Head-Fi.  Enjoy what your tastes tell you.

Can you compare the M50s with the newer HD558's?