I think you should get yourself the Amiron Home and give it a try. You can always return it for a refund if you don't like it. One thing that should be mentioned is that we all have a different shaped ear canal. Depending on the shape of the inside of the ear, that alone can cause certain frequencies to sound harsh for some people, and fine for other people. I did not find the DT1990 to be too bright when I tested it at my friend's place. I do not find my Amiron Home to be bright either. We did a listen a couple months ago just to compare the headphones. I had not heard the DT1990 before, and he had not heard the Amiron Home before. We both were able to identify that the upper frequencies on the Amiron Home had a smoother character. Neither of us found either headphone to be bright, harsh, or sibilant though. I used to own a DT770 250 Ohm a few years ago. That headphone has a nasty treble spike at 8-9kHz. I found it to be a terrible headphone in the upper frequencies. It gave me headaches and literally hurt my ears. There is a harsh and grainy character to the DT770 at 8-9kHz. I sold it, and later I got the DT880 250 Ohm. There was no more issue. It also has a spike at the same frequency, but it is so much cleaner and and refined. I did not find it harsh or fatiguing at all. It was much smoother. The frequency response graphs for headphones can give a general impression of what the headphone will sound like, but it will not tell the whole story. Take my experience for example with several Beyer headphones, which all have the peak at 8-9kHz.
DT770 = painful, headache causing
DT880 = detailed, articulate
T90 = painful, headache causing
DT1990 = detailed, articulate, more refined than the DT880
Amiron Home = very smooth, detailed, refined, cohesive
DT770 = painful, headache causing
DT880 = detailed, articulate
T90 = painful, headache causing
DT1990 = detailed, articulate, more refined than the DT880
Amiron Home = very smooth, detailed, refined, cohesive