After many hours of trial with different devices, I have pretty much settled with the EQ presets which sound best to my ears. Of course each DAPs have different EQ implementations so it's difficult to create an exact match that will make all DAPs sound the same with the iSine20.
But the idea is common for all DAPs (boost 100-200Hz and below by 6 dB cut between 1-2 Khz by 5 - 7dB then boost between 2 - 7 Khz by 12dB.) 8Khz and above usually doesn't need to be touched.
With iSine20 and EQ preset. It rendered my expensive ciems now virtually unlistenable. Switching from iSine20 then to any ciems I have it''s very clear to my ear that the iSine has much superior SQ. Timbre, clarity and imaging is more natural, and I think more precise with iSine20 and it makes my ciem sound artificial or lacking something somewhere. The iSine20 also appears to sound bigger and fuller. The only thing my ciem holds in their favor against iSine20 is isolation. But this is becoming moot, as I have been using the iSine20 while outside I have adjusted to it's open-back design. It doesn't seem to matter while in the mall or a coffee shop. It is only completely unusable inside a plane.
NT-6 which I considered the clarity, imaging, and detail champion feels like no match with the iSine20. If I switch between the 2, NT-6 now sound somewhat artificial. Though it can match extracting details after details with the iSine20. iSine20 just made me realize it's flaws (e.g. too short of a reverb in cymbals or not much depth on a kickdrum, etc.)
I think the iSine20 with EQ is comparable with my full-size headsets as far as SQ characteristics are concern. It actually takes some head-time away from my Aeon. I also think it can also hold it's own against my HD800, my Stax-007A or HE-6. I am not saying iSine20 is better than these legends but it has some of the best qualities of each of these headphones.
If I get stranded on an island, I think iSine20 is the only headphone I'm going to need.