so looking to get some new headphones and they must be over the ear and DO NOT want leather i would like a soft velvet for the ear pads. anyways i came down two these two headphones and i don't know if the HD 558 is worth the extra money? feel free to give your opinion or if you think i should go with something different? 
I would not spend the extra 40 on the 558s personally. But they are both good headphones.
I have the 558's and love them. Never tried the 518's though.
The 558's are easily moddable to 598's by the way. Which are €50 more expensive over here.