i have mainly been listening to the AD2000 lately, but my reference headphone for the last few years has been an HD-650, over that time i have removed the foam and grills, i added a cardas cable and recently modifed the enclusure to a more open design and that has helped lift the veil in the highs. over that evolution it has been the tone of the Senns that has kept me impressed and has motivated me to change experiment with the presentation.
i have owned the SA5000, K701, and Grado 325i. none of which could truely replace my Senns (the k701 was very close). now the AD2K has been the first headphone that i can say has been competitive and possibly better. AD2K are more detailed and dynamic, plus they have better balance top to bottom, they are not sibiblant, they dont introduce color but dont sound flat. i have not heard any other headphone that can approach the sheer power handling of the Senn HD line, the AD2k is close. the AD2k uses a mini-plug but i bought a W5000 cable from Audio Technica to remedy that, i havnt installed it yet so it doesnt affect my listening impressions. ( BTW the AD2K and W5k uses the same wire, they just terminate to different plugs)
i understand the price diifference is significant between the AD2K and the Beyers, i specified that i think its worth the extra cost. in the case of the Manufaktures they are about the same price. in the same tolken the Hd580 is about half price of the Beyers and i think they would be a better choice even at the same price. but i never hear that the Beyers are great headphones for the price, i hear they are great headphones. the resolution of both these Beyers does not compliment a resolving system enough, this could explain the polarizing opinions as i think they could make a modest system sound better by simply compensating for its own imbalance rather than accentuating flaws.
the DT-990 has stronger bass and recessed mids/highs, the same can be said about the HD650. the actual difference is that when i push the Senns to louder volumes to open up in the highs, the rest of the music follows suit in a linear way. the bass becomes amazingly articulate and can be delicate, the mids remain butter smooth and tonally satisfying, the highs are often desribed as veiled but they still have incredible detail retreaval and zero grain. as i push the DT-990 they simply boom more untill it overpowers the sound.
conversly, the DT880 exagerates the highs and recesses the mids and bass. if they were exceptional highs i would have kept them. they are not. IMHO they are generic and grainy. there is no way to dig up the body of the music with the DT880, the peaky highs limit the volume and headroom.