So compared to Sennheiser's HD555s.... how are these:

http://www.newegg.com/Product/Product.aspx?Item=N82E16826106515

The 558s. Newegg is out of 555s and it looks like wont be getting more in-stock. Is the 558 a slightly newer version and can be modded to a 598 like the 555 to 595?