Now the big reveal. I bought the Dusk, and I absolutely love them. I changed ear tips to AZLA Sedna Ear Fit Lights and I use the Dusk DSP Default tuning exclusively. I did find that tuning benefitted with some additional shelves, so using my USB Audio Player with its parametric EQ, I found I could add a +2db bass shelf at 200 hz and another +1 db shelf at 50 hz, and I also shelve everything above 400 hz down by half a db. In other words I added these shelves on top of the eq already on the cable by using the EQ program on my phone.
Doing that, the result is absolutely stunning. They just sound right to me--extremely detailed, great dynamics, powerful bass and zero harshness. The USB cable seems more than adequate for powering them, and I detect no issues with noise at all. Everything seems completely transparent.
I also bought a Hidesz S9 Pro Plus (Martha) from Ali Express. As of now, I can't duplicate the DSP tuning I'm getting using an analog cable and parametric EQ. Everything just seems a little off, but I'll keep experimenting.
My other two IEMs are the Simgot EA 500 LM and the Truthear x Crinacle Reds. Both of them are very good, but even with the eq's, neither sound as good as the Dusk. I'm using highly rated ear tips (Devinus Velvets for the Reds, and again Azla Sedna Lights for the LM's), and powering them with the Hidesz and using the EQ on USB Audio Player Pro. Again, they just both seem to fall short of the Dusk in resolution and natural tonality. Perhaps it has something to do with how they all fit in my ear, but I very clearly prefer the Dusk over both of the other two. Though none of them have a proper sound stage (they're IEMs, after all), I find the Dusk does have much more focused images. The images on the Red, in particular, seem notably diffuse.
I am also finding the Dusk seems to be able to play everything I want to listen to. I have no need to have one IEM for Jazz, a second for Classical, and a third for Rock. The Dusk just sounds correct and convincing on everything.
I don't know exactly why they seem to sound this correct to me. I'm sure if they were tested, they would do very well. I am, however, uncertain that the test results would shed much light on why I so strongly prefer them over my other two very good IEMs.
But I do.