I own both, I got the D2000's on a good deal last year and I love em. I've owned the HARX700's for a couple years or close to it now, did the foam mod and am in fact using them right now. I dug them out of the storage bin in the closet, and hung up the D2000's for a bit. I run them directly out of the HP jack on my Auzen X-Fi Forte, so no not an amazing amp, but it gets the job done for me and keeps desk-bound clutter to a minimum. But back to what I came to post here about, I believe that the D2000's do sound better overall and they should for the extra cost, but honestly I feel my pair of mildy modded HARX700's (foam pad mod and felt removal mod) are 75% there on the D2000's. I enjoy both, but the D2000's are lighter and vastly more comfortable (leaps and bounds)...not saying the 700's are horridly uncomfortable, but after being used to the D2000's comfort for so long the stock pads do in fact suck in my opinion. I may try lighter density foam under the pads to see if that helps a little bit. Another item is that my ears get hotter much sooner with the 700's, and I must remove them and take a break much sooner and more often than the D2000's.
I do feel the 700's are better suited to faster music, the bass is tighter overall, but the D2000's emphasize deeper bass. I also feel the D2000's have a crisper treble and upper mid sound, where the 700's is a tad dull in comparison, vocals are easy to hear on both, but the D2000's seems to bring out more in my music and games. Granted my source, eq tuning, listening preferences all play a part in my opinion. I really have enjoyed both. I don't like the hinges on the D2000's, they are sturdy, but it is a known weak spot and I've had no issues. They were easy as the 700's to adapt a mic to for Teamspeak/gaming. Again, the D2000's are much, much, much more comfortable, but is that worth the price difference to you? Every once in a while I consider selling my D2000's to try something new, maybe from the beyer line, but the 700's are staying and I may just mod them further someday. Definitely a solid value for the $30-40 range, I've yet to see another pair in that price range offer what these do and I've recommended them plenty of times with confidence.
I just wish I could mix the D2000's comfort and lightness with the RX700's value. I'd gladly pay $100 for such a combination. But honestly I'd rather find a pad replacement for the 700 than replace them in my collection. Cheers.