So I got the Denons today! Some quick impressions: very nice build quality, though the headband isn't as nice as my Sennheisers (which is odd, considering the Denons retail for double my HD555's). My lightly used D2000's arrived exactly as my seller described and with only a few dozen hours on them, they've just started to burn in. The cans I purchased came with the stock pads and the luxurious, svelte JMoney leather pads which are, to be honest, completely amazing. I had minor skin itching from them for about a minute and no heat/sweat problems.
And how do they sound (to me)? Fantastic. I was not prepared for the bass these things throw out. There are certain genres of music that I cannot play at a high enough volume to hear detail without risking my head exploding. Is that a negative thing? No, not really. I can just listen to something else or switch to my earbuds. For people who love their bass--although my ear is not trained enough to discuss anything about the bass' detail or speed--these cans will literally rock your head. With the JMoney pads, I was surprised at the soundstage, coming from my Sennheisers. It's actually pretty wide for closed cans, but then again, that may have something to do with the fact that the D2000's backs are basically just for looks. These phones leak in and out, as I had read while researching them. I don't blast my music, so the outward leakage will probably fade over a few feet and not be annoying to my future roommate, but they definitely missed the mark as far as what I was looking for. The inward leaking doesn't bother me much, but I should note that they barely isolate at all. The biggest thing they muffle is the sound of my keyboard, reducing it to dull key-hits without any of the higher frequency "clacking." Inward leaking doesn't bother me at all, though, as--once again--I'm coming from a pair of very open Sennheiser cans.
To sum up, I really like my Denon D2000's. I was offered a brilliant price for these cans in very much mint, pristine condition including the superb JMoney pads. The bass is a little too heavy for my tastes in certain songs, but it creates a full, awe-inspiring sound signature in almost all of my preferred genres. To my ear, the bass is not overpowering in most of the music I listen to; instead, I have a new-found appreciation for bass drums and guitar, among other sounds that fall into the lower registers. I find the D2000's to be very comfortable, light, and well-built. I am already considering some Lawton Audio mods in the future because I like so much about these cans. I should also note that my Nuforce uDAC drives these headphones just fine and sounds good, though I cannot comment if the two "compliment" each other due to my lack of experience with analytical listening.
These are not perfect headphones and their sound signature may not be for everyone, but if I'd auditioned them before buying, I am very sure that I would have picked them up anyway (especially at the price I got them). I look forward to picking up the burn in where the previous owner left off and keeping an eye on my wallet so that I can save up for some of the very tempting, awesome-looking mods at Lawton Audio for Denon headphones.
And yes, this is my idea of "quick" impressions. Thanks for everyone who helped me determine the proper cans for my needs and price range.