Thanks. I've read all of your comments throughout this thread. What are you referring to by "Dark"?
If you mean that upper mids and lower treble are slightly pushed back, that's a good thing for me. The M8 is actually a little brighter than I prefer. I also appreciate a little bit extra from the low frequencies, so long as it doesn't stampede over the lower mids. Do you find the M15s or the M8 to have better resolution and air? Unfortunately, the M9 is prices in above my budget. Perhaps some day.
The m15s is a little bit darker in a sence, less resolution then say a m8. I do say the m8 is a little brighter (but that is also very headphone/iem dependant).
Reading what you wrote, the m15s could be in your park. It gives a little more low punch. I would say a tweaked M15. But in my opinion that bleeds just a little bit in the mids, but it could match perfectly with you headphones, hard to say.
Resolution m8 wins, easily.
I would highly recommend you to take a astell and kern with a AK dac as a option too. Something like a se180 with sem4 (sem4 sounds amazing!) dac, or a astell and kern se200, or the new ‘kann max’ from astell.
De Fiio give a lot of bang for the buck, and it is certainly not a bad deal, but still have to hear the first natural sounding one from them. I would recommend ordering one from amazon (so if you don’t like it can return).
The best natural sounding daps to me where Lotoo gold, everything from astell and shanling.
I bought a se180 in the end, maybe they don’t have the most fancy interfaces or options, but man does it sound sweetttt, punch, air, never harsh. with a sem4.
(The first time I thought this is on level of my chord qutest with my burson 3xrgt, with way less power ofcourse but portable) even de included sem1 sounds amazing.
I already can see myself owning something like a sp3000.