I also miss more bands in my ADI-2 DAC. I wonder what the reason is for the current band limit and if RME could add more via firmware.

The limit is connected to the sample rate.
Below 192 kHz the DSP has spare power.

Let’s put it this way -

Why are narrowband EQ corrections with foreign origin questionable and should be just left away?
ALL the measurement-based EQ curves from the internet are wrong above ca. 2-3 kHz, with very few single exceptions.

The measurement systems used do not supply data with a high enough VALID frequency resolution to justify narrow EQ bands.
You cannot EQ better than your measurement is.

One has to be aware of the limits of a measurement system to judge it’s results.
If you compensate above these limits you introduce errors, and leave the errors you want to compensate untouched.

• Even slight changes in headphone’s placement, on your head or the measurement coupler, yield totally different results for frequencies above ca. 2 kHz.
Which one to use then, and why?
Averaging various positions doesn’t help much, practically you don’t listen to an average, but a discrete positioning.

• The famous “Harman”- and other compensations are strongly smoothed, coarse approximations for a very certain setup, intentionally leaving out the fine details of the curve, therefore limit frequency dependent precision.

• People use Harman- or other compensations as if they were valid for other measurement rigs too, which they aren’t.

• Most compensations, except “Freefield” do use the room sound signals without any angular weighting.
Opposed to that the human brain does give a lot more weight to the direct sound from the source, above the room-reflected sounds.

• Your personal pinnae have different shapes, and therefore different HRTF (Head Related Transfer Function, angle dependent frequency response) than the measurement “ear”, coupler.

• Each human’s auditorial system permanently adapts to the sound colors it’s presented, like the eye adapts to light colors.
You have to “readjust” that from time to time with natural sounds to judge an artificial reproduction system.
The amount of ability for those adaptions is different for each individual, and there are limits.

• There are certain characteristics of a headphone or loudspeaker that are prominent and specific enough worth for correction, the famous 6 kHz peak of Sennheiser’s HD-800 comes into mind.
Even this one doesn’t annoy everybody.

Remark:
Didn ‘t you notice, all these Oratory, Auto EQ Project and most other Internet fine-tweak-EQ Setups simply sound like shit (sorry for the strong word) in the upper range?
Doesn't a simple Treble Shelf EQ or broadband Peak EQ, or a combination of both, adjusted to taste, give better results?

The measurements, BTW, can give a starting point for COARSE correction above 2 kHz, and below 2kHz measurements actually are quite valid, if your can achieve a good seal on your head.

Finally:
I do my EQs based on measurements on my own head, using my own compensation curve.
Even this is limited and has to be adjusted by taste over a period of several weeks or months at least.

I have to admit that for laymen this measurement thing is hard to understand.
With headphones even experts often aren’t aware of full problematic.

The central point is the precision and resolution of the target curve, and this has nothing to do with the measurement’s sample rate.

The popular Harman Target curve is a more or less hand-drawn (really!) average with a resolution of less than one octave.
This would equal a Q-factor of an EQ-band of about 0.7 or less.

No measurement-based EQ with higher Q-factor can be justified on this base.
It will just introduce errors, instead of corrections.

And this is only one of the factors I listed above.

Tuning an EQ by listening is not that complicated.
You have to ask yourself if each EQ change is for the better or the worse, like or dislike, while listening and comparing over a period of time.

I have seen your newly released remote control 2.0, which is very awesome. I would like to express my sincere gratitude.
Closer to home, 7-bands eq are not enough.  For example, my headphones 7506, according to what you said before, seem to require 9 segments.  What's more, I believe many people will use it to connect speakers, which requires calibration of the room. The acoustic performance of different rooms varies widely, so I think it is necessary to add a few eqs（such as 10-bands or more）.  And it may not be too difficult for you, as long as it is limited to less than or equal to 96khz or 48khz. I hope you can take my advice.
By the way, I don’t seem to see the Preamp gain function in eq. Can it be added?

The Sony MDR-7506 - if you have the original, not a Chinese copy(*1) - is a perfect example for what I said above.
I do use it in my studio quite often and:

It does not need any correction at all, as it‘s perfectly tuned to listen at studio level.
If it sounds too bright, you’re listening too loud.

The only thing it needs is replacement of earpads every two years, as their faux leather starts flaking soon, which changes their sound to non-existent bass.

PEQ-Preamp-Gain is abandoned, because ADI-2 has an internal headroom of 24 dB that prevents clipping.
Simply bringing down the Volume control therefore is fully sufficient to avoid overdrive.

(*1) Regarding fraudulent Chinese copies that flooded the market for the Sony MDR-7506:
Look at the driver side (with the earpads removed) and mostly you can tell them apart.
The original has a perforated metal dome at the driver mount.
The copies often just have a flat plastic soundboard.
Another signs: the cable and the earpads of the copies are quite stiff.
The earpads miss the rubber bands that holds them in the gaps.

The Chinese counterfeits sound like s**t BTW.
I have some that I finally paid nothing for, as I forced a full refund.

https://www.expandore.com/articles/Bewa … adsets.htm

When listening not too loud, at “healthy“ long term listening levels, Sony MDR 7506’s bass and treble sounds correct for me.

If you have too much bass, simply remove the flaky fake-leather on (not too much) worn earpads.
Rip it off with sticky tape.
The cloth underneath is comfortable, and the little sound-leak reduces the bass.

I think I already explained it:

The Sony MDR 7506 are pro audio headphones.

A pro listens much longer per day, therefore tends to listen at lower levels than the average home user.
This is essential if you choose to do audio as a lifelong job, not to have to stop it half way through the career because of loss of hearing.

Now listening lower, the 7506’s bass and slight treble boosts keep the spectral balance according to Fletcher/Munson‘s curves, think “loudness correction“.

I wouldn‘t suggest the 7506 as reference ‘phones for mixing and mastering.
But as control and editing‘phones for raw, unprocessed signals e.g. they are great.

And no, I’m not referring to measurements (from my supervisor???), but my own experience.

Remove the earpads, then the 4 screws that become visible.

When remounting, be careful to not strip the plastic threads, don‘t over-tighten the screws.