I have these, driven by a Ratoc mid-fi DAC/Amp (50.000 Yen), listening to FLAC 24/96 or upscaled 12/44.
 
I can compare them to the W1000X which I also purchased recently, to the AD900 and to the AD700. Most of my impressions AD900 are the review for those cans. 
 
I can say that the AD2000 are by far the best headphones I have listened to so far. They are not nearly as airy and whispery sounding as the AD900/AD700 but are very forward, aggressive and fast. As far as I can tell they are also superior in almost any aspect to the W1000X. It could be the strong clamp (which can be alleviated by bending them a bit, no harm done) but they just sound unbelievably tight, tight, tight!
 
I thought I could never understand the term of speed regarding headphones but these are really different. They don't share the sometimes piercing high frequency problems of the W1000X but stay very evenly loud along the frequencies. 
 
That being said I think their aggressiveness, while giving a very dynamic listeing experience, might be a little fatiguing for people who prefer a laid back sound. 
 
I think these cans excel at almost any genre but are particularly suited for electronic and classical music. Given their speed they might work very well for rock/metal as well. I think I would actually prefer the W1000X (equalized) for Jazz recordings as their sound is a lot more relaxed and laid back. I can not imagine myself listening uninterrupted for a long time with the AD2000. Also, having my ears touching the drivers is quite uncomfortable so I might upgrade these with some sort of mod or maybe even other pads.

These are great headphones for quite a budget price (at least in Japan and America). 
I also own the AD2000 and the W1000X so here is a little comparison:
 
The W1000X would be the warmest sounding of the bunch. The AD900s openness also takes away something from the bass area that would be needed for a warm and embracing sound. The AD2000 is airy as well, but a lot closer and tighter than the AD900. In direct comparison the AD900 seems to be rather muddy with not quite as clear mids and highs than the AD2000 or W1000X. Whereas the AD2000 doesn't seem to be needing any amplification (of course it scales well), I would highly recommend to amplify the AD900. Comfortwise it's en par with the W1000X or maybe even better, considering that the W1000Xs pleather pads can get pretty hot on the ears. Listening to the AD900 I can understand people complaining about a certain detachment from the music, as if one is floating in outer space with the music being everywhere. If that is not your cup of tea, better stay away. All in all the AD900 is extremly non-fatiguing even at higher volumes. The W1000X has to be seriously EQed before being comfortable for longer sessions and even the AD2000 needs some adjustment at higher frequencies for that. The slight muddiness of the AD900 on the other hand let's you dive right in without any adjustments at all. I like Audio Technicas adapter to 1/4 a lot, it's a sturdy unobstrusive construction. 
I can highly recommend the AD900 to anyone listening on a budget and preferring a translucent and open soundstage.
Great for classical music, might not work as well for close quarter chamber music or tight cellar jazz recordings though. It's pretty good for electronic stuff as well, mind the lack of bass though.

 
So I bought the Ratoc Systems RAL-2496UT1 on the Japanese Yahoo Auctions site a few days back. It has been getting 100% positive reviews on Amazon Japan and Kakaku.com so I thought it couln't be bad. Also, the guy selling it sold his Beyerdynamic T1 and A1 at the same time so he probably used the RAL-2496UT1 as well and knew quality. 
There is virtually no information on any non-Japanese website whatsoever so I decided to review it here. The RAL-2496UT1 goes for a retail price of 54,000 Yen (700 Dollar) which is quite hefty. I managed to get it in sparkling condition for 15,000 Yen so it was quite a bargain.
 
Now I must admit that I'm not very experienced with the hi-fi/audiophile terminology and that I never listened to really high-end hardware, so please be gentle. I will keep this review as short as possible.
 
The RAL-2496UT1 will be compared to my Fiio E10. For headphones I will be using the Sony XBA-3 IEM, the Audio Technica W1000X and the Audio Technica ATH-AD900. I used MusicBee with WASAPI and mainly FLAC material in 24/96 or SACD-Rips with Foobar. I just got about 3 hours with the RAL-2496UT1 so I might edit this review later at some point. Listened mainly to contemporary classical, jazz and electronic music.
 
 
-- Build Quality/Design --
The housing of the RAL-2496UT1 is fully metal, with a brushed aluminium front. No plastic at all. As you can see on the last picture, the volume knob does have an additional hole for something to screw in there. I guess it must be some sort of stick to drive the volume more easily. It feels pretty solid albeit not as compact and bricky as the E10. The volume knob turns a little to easy and plasticky for my taste which is something I would not expect from a 700$ device.
I like the design, although not special it's far from being dull. The 3,5mm headphone jack is a little recessed which could make it difficult with some larger headphone plugs.
A very nice feature are the LEDs on the front that show you the frequency of the material being played dynamically. It does switch from one song to the next depending on your source material. 
 
-- Sound Quality --
As far as I can tell the RAL-2496UT1 pretty much crushes the E10 in terms of sound quality. Especially the basses seem to be more fluid more oily and smooth without loosing detail. Overall the E10 sounds execptionally flat in comparison. Something that bothered me is the constant static noise. It's not really noticeable if you don't use IEMs and play music but it's there as soon as there is no music playing. I doubt that this really degrades audio quality but considering that the E10 is dead silent it seems like an issue to me. I haven't been able to use the line out, coaxial or optical outputs yet so it might be an issue with the headphone jack for all I know. 
 
-- Other stuff -- 
The RAL-2496UT1 has considerably less amping power than the E10 so anyone looking to pair it with a power hungry headphone without a dedicated amp, look elsewhere. The W1000X are very easy to drive but I would have to almost max out the volume on the RAL-2496UT1 to listen at higher volume levels. It does not have a dedicated power supply and is powered via USB only. With this it might even qualify as  something one might take on the road.
 
 
Overall I would have been quite unhappy, had I spent 700 bucks on this. You can get it for about 450 on kakaku.com but I think even that might be a tad much. Getting it for 180$ was quite a bargain though and this will be my main DAC for some time to come. It might have to be paired with a high-quality amp as I guess thats what the guy I bought it from did with his A1.
 
Edit:
I have been using this baby for about half a year now and I find it incredibly smooth and easy to listen to. It does seem to have a very slight bias towards the lower frequencies, making it very musically. I think this is an ideal partner for low impedance headphones like many of the Audio-Technica ones (using it with W1000x and AD2000). I can now also say that the noise is a non-issue. The E10 switches itself off when not playing anything which is the reason I haven't been hearing any noise. The RAL-2496UT1 is actually very silent and does not have a lot of background static noise.

Really wanting to buy the AD2000 I got the W1000x on the Japanese Yahoo Auction site for a ridiculously low price of 29000 yen. They are used but have almost no wear or tear. I guess they have been broken in alreay, but I really can't say. The might have been used as an exposition model since the plug doesn't show any wear.
 
Using my Sony XBA-3 in the office most of the time, I found the W1000X not as immersive as I would have liked. IEMs make me feel a lot more "inside" the music. 
 
The worst thing that's keeping me from using these "closed" cans everyday is the VERY bad leakage. Sitting in a cubicled office these would annoy everyone else when using them at medium-high volume. 
 
That being said, these cans are exeptionally detailed and clear sounding to me. I'm new to the audiophile world but I think this is what people refer to as "soundstage": The instruments seem to be quite distant from me. Much more than with the AD2000, although those are open and airy they immerse me much more in the music. The highs started to hurt my ears when played at higher volume.
 
Listening to mainly classical (contemporary and baroque), Jazz (hard-bop, impro, contemporary, big band) and electronic music via my RAL-2496UT1 DAC using MusicBee with WASAPI output and mostly 24/96 or upscaled FLAC material.
 
Now I haven't got more than one or two hours with these so I might edit my review later but the leakage is real and quite noticable for closed cans. So anyone looking for a good seal, please look elsewhere.
 
Edit: After listening some more I am tempted to sell these since the pleatherpads get way too hot for my taste. 
 
Edit no. 2: I actually replaced the pleather pads with the L3000 lamp leather pads without a problem. They are a pricey upgrade (60 dollars) but worth every penny as I can listen to the W1000X without problems for hours now. They comfort has definetly improved by miles. Also I would advise to equalize these cans according to this thread: http://www.head-fi.org/t/413900/how-to-equalize-your-headphones-a-tutorial It has made mine a lot easier to listen to since they have quite some spikes in the upper frequency ranges.
 
Edit no. 3: I have been using the W1000X for about half a year now and I am using it together with the AD2000, mainly switching for issues of comfort or musical genre. It's an awesome headphone and I am VERY satisfied with my purchase.