Don't worry about trying my settings out, yours is very similar and sounds great.
Here's the measurements for the iSine 20: https://www.innerfidelity.com/images/AudezeiSine20.pdf
All I did was try and compensate values for the iSine 20 to sound like an HD600 found here: https://www.innerfidelity.com/images/SennheiserHD600.pdf
Here's what I found when equalizing the iSine 20.
50hz low shelf filter by 14db gives off the impression that there's bass except when called for. Good side is that this increase is not invasive unless if the recording calls for it.
100hz -> 500hz thickens the mids, it sounds good with the HD600 but not so much the iSine 20.
800hz -> 1000hz needs a slight reduction, as this area tends to make the mids honky. I cheated and made a slight dip in 1khz, so I can keep the volume between 800-900hz to keep the mids forward.
1000hz-> 1500hz hazes the mids, makes brass instruments honky and vocals tinny.
2000hz seems to be fine, this should be left untouched from my adjusments
2500hz needs a slight increase, as this gives female vocals the sweetness I desire
3000hz -> 4000hz increase is desired, as it brightens up vocals. I like brighter sounding headphones.
4000hz -> 5000hz increase was desired, this brightens up violins, I recently reduced mine as violins were slightly too resonant
5500hz was slightly reduced to avoid grainy mids and reduce fatigue from the bright mids I set up
6500hz was increased to give airy mids
9000hz slightly increased to give treble texture
10000hz reduced to remove metallic treble
17000hz increased for extra sparkle
20000hz increased for airy treble and extension.
Thats a good brief for a beginner like me to understand how eq works, so thanks for that.
Also, after checking the countless eq photos i took out of this thread, i think the one iam currently on is the original cipher replica posted by @KMann (thanks to him)
One more thing, i see now why iam not hearing any recessed vocals, because you misread the 6db to -6db at 2540 hz, i now think at 6db is a bit shouty so i might lower it a bit to 5 or 4 db and see how it compares ..