How exactly do you “power match” a headphone that takes literal miliwatts to reach 110dB SPL?

Julian Krause tested the SSL 2 along with its headphone output. Assuming the headphone output on the SSL 2+ is the same:

it’s output impedance is low enough to not change the frequency response of the 6XX,

• distortion is pretty bad at low impedance loads, but is good enough at 300 Ohm,
• all other parameters are not an issue.

So the amplification is good enough.

I think you would benefit the most from EQ. I suggest the preset from oratory1990: https://www.dropbox.com/s/qs4hs92tvfbwr04/Sennheiser HD650.pdf?dl=0

Outside of that, the things he did say that were controversial, he apologized for, stating that he wasn’t very familiar with internet culture, and didn’t know he would upset others.

He didn’t know that he would upset people by being a racist twat, sending death threats to a reviewer or being a terrible human being overall?

It is, but the changes are in 99% of cases so minuscule that it’s meaningless.

If you had 2 pairs of the same headphones or speakers you would know.

2 pairs of the same headphone or speaker don’t ever sound exactly the same.

If you want to get them to 130 dB - yes. Exponential growth goes wild.

This audeze article does a better job explaining the terms and how they relate to each with regards to how much power is needed better than I ever could.

It kinda does but IMO only to a point. And that point is where they claim that your amplifier should be able to handle transients that are 50 dB louder than the average SPL.

It would mean that if you listen to music at an average SPL of 80 dB, your amplifier should be able to output enough power for peaks up to 130 dB.

Let me give you some examples of how much power would that be for some headphones (based on measurements from SoundStage Network or RAA):

~60 mW for very sensitive IEMs like KZ CRN.

~1.3 W(!) for a low sensitivity planar IEM like 7Hz Timeless.

~1 W for popular sensitive headphones like ATH M50x.

~126 W (a hundred and twenty six Watts) for one of the least sensitive headphones on the market like Hifiman HE6se.