Yesterday I could hear the Oriolus Reborn and the Acoustune hs1670ss. I didn't make a direct comparison because I didn't have much time, but I trust my auditory memory with the week I've been listening to dk2001.
The oriolus reborn has the mids at a very similar distance than the dk2001, the difference is that the Oriolus has more meat and its means are richer and more addictive, but at the level of details I would say that they are very close, even the dk2001 in this section It sounds somewhat clearer but at the expense of the richness of the oriolus. The bass of the oriolus also pursues the style of its mids, they are large, close and hit with authority but they maintain a good general control, and here I get the feeling that the dunu is more honest and does not saturate the bass so much to maintain an equal sound of controlled but cleaner in general. In terms of treble, the oriolus has them present but softened like silk, the dunu sounds a bit thinner here but I feel that the level of separation and air they achieve is at a very similar, but again the dunu sounds lighter and somewhat refreshing.
With regard to Acoustune, these do make a clearer difference. They are fast, very fast, they resolve details much more easily, they have a higher level of transparency. The bass sounds tight all the time and reproduces more information across the spectrum. The mids here moves a little more back than the oriolus and the dunu, but they are cleaner and more natural. The highs here shine and have a better extension, granting a new level of spatiality and separation.
I feel that the dunu is at a similar technical level than the Oriolus. With the Acoustune it does mark a bigger gap, but it is not like a day and night either, I can go back to the dunu and continue enjoying it all the time. The dk2001 remains at a very good level compared to these significantly more expensive iem, and that is appreciated.