I had the hd600 for many years. It has a slight upper mids emphasis and no low bass. The 58x is smoother in the upper mids and to my ears more tonally correct. On the bass response is no contest. The 58x wins hands down. I like also the soundstage better on the 58x. The hd600 is perhaps a bit more resolving, not by much. If your ears are used to the bright upper mids of the hd600, you need some time to adjust to a darker presentation.