With my RX900s, I've never noticed any improvement with the addition of an amp. I did just tried out some Black Sun Empire and feel that, the RX900: A. Needs to be closer rather than further from your ear (so that excludes the ear pad mod) B. Needs a bit more and quicker bass. My Ultrasones sound much better with Drum N Bass. They go deep, are quick, and can be prominent when needed. I would look for some HFI-580 honestly.
The RX900 are great on slower genres, but the Drum N Bass I tried were just too fast for them. I'm not sure how the A700 would fair against them in that regard. Let me give my M50 a try, as I think those may be well suited cans.
M50/HFI580: Just tried out the M50 and HFI-580 and the M50 definitely have the same kind of slow bass that the RX900 have, though they go deeper, are a bit quicker and are more detailed (and also sound more realistic). I would personally look at some phones that are comparable to the HFI-580. Some people may chime in and say bassier Grado might work best. I can't really comment on that though, as I still haven't listen to any Grado. From what I've read (and feel free to research yourself), Grados will have a similar forward sound to them. I really don't have the first clue as to what model (mod) will give the Grado bass you are looking for, and whether it is a fast enough bass.
Shure SRH750DJ: I also just tried out my Shure SRH750DJ, and those do have a fairly fun bass quality to them as well. And don't seem to have to much trouble keeping up with the fast approach of music. I'm going to try out some more headphones though. Probably some Sennheiser HD485, Maudio Q40 and Ultrasone Pro900. I expect all of them to do something quite involving with the music, but who knows, it may really add to the music!
M-Audio Q40: The M-Audio Q40 definitely have an advantage, in that they are bass oriented phones. What I like is they are easily capable of playing some of the lowest bass I've heard on headphones, while still paying attention to the rest of the bass detail and representation, all while not completely drowning out mids and highs. The mids and highs are actually still fairly pleasing, but I would never say they are great compared to a number of other headphones (though in all fairness, I think they are better than many other "bass" headphones). What I like about the Q40, is that you can distinguish all of the low end, all the time. There seems to be a bit of low low bass lingering in some tracks, but you can still depict the rest of the higher frequency bass just fine, and with great detail and adequate speed.
PRO 900: I don't find some of the signatures of the PRO 900 to be conducive for Drum N' Bass, but I think this is part of my tastes. What I get from my PRO 900 is a very airy sound compared to other closed phones, seeming as if they are open back phones. I think where the PRO 900s shine is with their all around detail. The bass is definitely there, but the airy nature forces it to feel a bit more distant. I still think these headphones could use some modding, a bit more clamping force and earpads other than stock to give a bit more refined bass quality. The soundstage (artificial some will say, but fun none the less) and brilliant detail with a very "fun sharp" nature (It is tough to describe, but sharp is sometimes a shrill high, but in these phones it takes some adjusting and appreciation to really find their involving aspect). I really want to try some more modding with these phones and maybe a different amp, and see if that can give some more refinement in the bass, as I think the high-mids and highs are absolutely brilliant on these headphones!
Sennheiser HD485: With the Sennheiser HD485, I've had some fairly indifferent feelings about them all around. They have a very unique sound to them, particularly in where the sound seems to be coming from. Out of all the headphones I've had, I think these would take the longest to adjust to in order to benefit from their unique sound. Now this may just be from the open back design, but it so much different from my other headphones. The soundstage is like none I've heard, not in that its spectacular, but in that it seems to be again, unique. It sounds artificial to my ears, but I can't really say that's bad. I know some people really love these headphones, and I feel that comes in time with adjusting to their sound. They don't have quite the slam factor that some of the other headphones have, but they aren't exactly bass shy by any means. I would attribute this slam factor having to do again with the open back design and the ear padding material. I've always felt that pleather/leather/etc (non-velour/velvet) gives more impactful bass. I believe the PRO 900 could benefit from this, and the DT770 are kind of an oddball in that department, all though I really want to give some pleather/leather padding a try on them.
Small Note of DT770: One thing I should also mention, is that I think properly amped DT770 could really do what you want. Now, it has been a while since I've had my DT770 (and I'm actually waiting for some in the mail
). I think, seeing as my music tastes have changed since last having them, my view of them will need to get updated. I know I've ready many more times than just once, that the DT770 are awesome for Drum N Bass. What version of DT770 and what amp you use (and using one is a must to get what you need from them, for DnB), you may get what you are looking for.
I think that is about all the testing I can provide for you right now, also considering this has almost turned into a mini-review
I'll be happy to answer any other questions you may have however
