You can mark me down as another person who is dissatisfied with the bass on the D2k's. Though I feel like my experiences are different still than most in here. I've had my Denons for around a year now, I've never been completely satisfied with them, but life had been so busy with moving around between jobs, and funds were so tight that I didn't have time to really explore why until now.
I've spent the last several days going back and forth between my D2k's, my Triple Fi 10's and a friends M50's on a variety of songs to try and pinpoint what it was that wasn't satisfying my listening needs on the Denons..
I initially knew I was dissatisfied with the bass, especially compared to the praise that is usually thrown upon them. I initially wrote it off as there wasn't enough bass for me, despite being far from a basshead. I've come to realize that the bass is certainly there, it's just not presented as I want it to be. I don't listen to much Techno, but I do listen to a lot of electronic-fusion, nu-jazz and electronic fused with hip hop beats or rock instruments (RJD2, Quantic, Inf, Thievery Corp, etc).
I feel like with most of these songs, the sub-bass is almost always present in the background in the recordings and it results an ever-present, farting rumble with the Denons. The sub-bass is more forward than it should be and less controlled. On some songs it almost feels like it's rattling your head, not necessarily in a good way as I feel the Triple Fi's had more power in the sub-bass but without the rattling.
Mid-bass is what is most important to me, I'm a glutton for bass guitars, songs with funky twanging and plucking bass strings. Red Hot Chili Peppers, SMV, James Brown, etc. This is where I initially knew I wasn't satisfied with the Denons as I knew the enjoyment I could get out of SMV's dueling bass guitar solos and I never experienced it with the Denons. Going between the TF-10s and D2k's it was immediately apparent the difference. The D2k's emphasized the low end bass strums which again sounded more like a farting noise than a bass strum, and also the hi-hat hits were brought far more forward over the guitars in a distracting way. With the Triple Fi's the bass guitars had the a far more authoritative sound, the string plucks were deeper and had a far more satisfying reverb. With the Denons the bass guitars sounded almost twangy by comparison, more like a Banjo than a bass. With the Chili Peppers, Flea's bass lines are supposed to be prominent, just below the vocals, with the Triple Fi's I get this. With the Denons you can certainly pick out the bass line but it's muffled by other things like cymbol crashes and backup vocals.
I don't mean to completely put down the Denons, there is certainly quality there. I don't find the mid's recessed as I've seen others say, I think the mids just gets drowned out in certain songs by the rumbling, uncontrolled bass and excessively sharp highs. When I listen to songs where I'm less concerned about a prominent Bass guitar or high energy bass beats like with Jeff Beck or Ben Harper, I think the Denons handle them beautifully, if with a little less-energy than I'd like.
I certainly don't claim to be an experienced audio expert, but I find it really surprising to see so much undisputed praise about the D2k's, I really thought there was something wrong with me for not being as excited or fulfilled from them. There are a few threads like this one though, I just have to figure that it comes down to differences in the type of music people are listening to, and/or personal preference. Even taking that into account though, I can't help but feel the Denons are a little over-hyped by some people. Maybe there just aren't enough suitable contenders at this price range that don't over color the music in one way or another.
