Keep in mind that the DT 990 is sibilant even to people who like treble-forward headphones. It's not a headphone for everyone.

Also the DT 990 pads are notorious for wearing out quickly. I have to change the pass on mine every 2 to 3 months as they become so flat, the driver cover starts pressing on my ears. This doesn't apply to the DT 770 as the pads have a stiffer foam on the inside. In comparison, my HD 599 pads last about a year and a half before I need to replace them.