Not directly, but the 627 and 8610 were the first opamps I owned along w/ the 209 which crushed both on technical merit.  I then sold the 627 and 8610.  The 627 is really about coloration and warming things up, it did not sound ideal in the Leckerton.  I'd only consider it to try to balance out a bright/thin IEM/phone if you were dedicated to the IEM/phone in question for some reason.

Good luck trying to hear a minimal difference in the noise floor - since that's all there is to it.

Hey, it might be audible with sensitive low impedance IEMs or at huge gain.
What it won't have is any extra quality that's not associated with noise floor.

OPA627 is really sweet and involving with the Audio Technica ATH-CKS1000, since this IEM seems to show the 627 bass quality quite a lot more than usual.

This just shows how transducers can influence opinion, since they are different in various ways and none are truly transparent.

The FR measurements of the CKS1000 at Seeko really don't tell the story of this IEM, I don't even like bass, usually.

Maybe it's because we're less interested in lording one over another?

I'm considering replacing the ADA4898s with something less power-hungry in the Leckerton, on par with OPA209 both in power use and sonically.
Any recommendations? OPA209 is of course out, that one is way too sensitive to cellphones.

ADA4898 (~8 mA/ch) is about as power hungry as AD797 (~8 mA/ch) or OPA627 (~ 7 mA/ch), which reduces UHA-6s mkII to ~8 hours instead of 24+ hours w/ OPA209 (~2.5 mA/ch).
Plus that one is rather bass-oriented, it sounds like a FET opamp with a bit different (less "oily") timbre, but it's not specified which input stage. Likely JFET.

AD8610s are more "upper midrange" from my experience than I'd like, but they are 3 mA/ch, close to OPA209.
How is ADA4627 sounding in that amp? Looks like ~7.5 mA/ch; on par with ADA4898, too short.

Anything else?