Ok, time to report my results with Dt1990. Using both the analytical and balanced pads as well as the Dekoni Elite velour pads, I can confidently say I prefer the analytical pads because of the clarity throughout the entire frequency band. It's some of the best mid-frequency band I have ever heard. The treble is also really great. The only area that seems to lack in comparison is the bass, and that is only because I am comparing to some planar headphones I have that have almost perfectly flat and tight bass down to 15Hz. But the bass is still better than any other dynamic headphone I have heard.
I do use a piece of felt cut into a circle and stuffed into each of the cups when I use these to reduce the extra energy in the treble region. Without the felt pieces, I get ear fatigue within about 15-25 minutes. With them, I can listen to music or podcasts or whatever for as long as I want without fatigue. The change is extremely minimal and seems to only affect the portion of the treble region that bothers me. But even without the felt, these are NOT sibilant. Sibilance in a headphone by my definition is where the sibilant region 5~8k has audible distortion or ringing, causing sounds in that region to be harsher than they actually are in the recording. What I DO hear is an elevated frequency spike in that area, but not distortion. It's very clear. . .just too loud. My planars with the "perfect bass" on the other hand ARE sibilant, even though they are noticably less elevated in that same frequency band. So "S" sounds are harsher on the planars, but louder on the 1990s.
Moving on. The Elite Velour pads have AMAZING BASS! Everything just feels so warm and inviting when listening through the Elite Velour Pads. The problem is music that is mixed and mastered VERY well always sounds better through the Analytical pads. But music that was maybe not quite as well recorded/produced tends to sound better through the Elite Velours. Regardless, vocals ALWAYS sound better through the analytical pads even without the felt.
As for the balanced pads, they are trash. I find them unlistenable. The sound is too far distorted from the original content. If I wanted to listen to music that sounds completely different, I would find different music. I think It ruins the sound. The Elite Velours give as much of a bass boost as I think is appropriate on this headphone.