ALMGNOONthe 990 80ohms sound wider and more detail on the highs, 58x better on Mid and vocal present. but it has a 3 blob imagery. You need to remove the outside foam padding to reach full potential. Lastly, the 58x is 150 ohms. will take more amp to drive. with that said, most amp can handle the 58x just fine. I feel the 990 is more dynamic, and more fun. while the 58x is a focus headphone. Not as much as the 6xx.