I've benefited from some advice on Head-fi in the past, but I'm not often in much of a position to contribute. However, I thought I might be able to add something useful to the discussion of the DK-3001 iems. I listen mainly to classical music, which seems less common amongst people posting comments on head-fi. This isn't a review, but rather a perspective, I guess you might say. My listening has been done through an Aune M1s, and I'm reporting impressions based mainly on high quality files of audiophile oriented recordings. I've listened to lots of other music on them, but I don't have anything special to add that hasn't been said upthread.
Classical music uses a very broad spectrum of frequencies. Tubas, concert grand pianos, and pipe organs all have notes with fundamentals in the 20-30 hz range. Even a contrabass bassoon reaches down to around 30 hz, as does a concert string contrabass. Jazz contrabasses and electric bass guitars have their lowest notes at around 40hz. Of course, electronic music can go very low, but for acoustic or electrically amplified music, classical very often has the broadest spectrum. This, and the sometimes resonant performances spaces in which it is performed pose some challenges for high quality reproduction.
Setting aside questions of fidelity, however one wants to understand the term, I often find listening to classical music that uses low-pitched instruments somewhat unsatisfying on iems, and on some headphones. Some are conspicuously bass heavy, and the balance doesn't sound natural. Others simply cannot produce sounds in the way that one experiences them to sound at a live performance. If the goal of high-end audio is to bring you to the concert rather than the concert to you, then these are closer to high-end for well recorded acoustic music than other sub-$600 iems I've owned or heard (which is to say all the iems I've heard, as they've all been under $600).
As for the overall sound, it's what people in the loudspeaker stereo world of the early 2000s would have described as 'euphonic', at least to my ears. They are slightly warm in character and provide a pleasing presentation of human vocals, male and female. I've enjoyed listening to polyphonic choral music with them quite a bit. For voices and instruments, they have a natural, but slightly less than accurate, sound. At the same time, the DK-3001s are accurate enough to make low quality recordings sound low quality and good quality recordings sound good quality. They do a good job with instrument separation, even in complex music, and they're one of the few iems I've personally heard (again, not a giant or especially illustrious list) that do not muddy up very complex contemporary symphonic music. One of their best qualities is relaying the resonant character of acoustic instruments. I notice this with jazz basses and acoustic guitars. They can produce a big enough soundstage to keep things sonically uncluttered.
There are no doubt better sounding iems in various ways. These sacrifice some accuracy for euphony. It's not always a trade-off I would favour. Nonetheless these bring me close to the music and closer to the concert experience than other pairs of iems that I've owned or listened to. I found these as a discounted ex-demo unit. The Aune M1s came at a decent price, too. While still not inexpensive as a combo even with the discounts, together they produce a lot of good quality sound for the money, and it's highly portable sound at that. I hesitate to recommend anything to others, but if one has the chance, I believe the DK-3001 is at least worth an audition for those who like live classical music.