Not to knock headphone science, I mean if it weren't for science and measurement then we wouldn't have nice dac and nice amp like we have today.
I guess it only bugs me when the measurement crowd stops at "it measures bad so I don't even need to listen".
As with everything in life we need to do things moderation. For example I like my coffee and tea with sugar and cream. But the purists might argue "you should drink your coffee black as how the barista intended". But I like how my coffee taste with sugar and cream. And I guess it's impossible to tell scientifically if that I will like my coffee/tea better with 2 sugar 2 cream, or 3 sugar 3 cream? Or 100 sugar 100 cream? Again...... moderation and to taste.......
Anyway...... I sidetracked a bit. Now back to point, I have Project Solstice hybrid tube amp. It has 3 output impedance setting that you can switch on the fly.
Project Solstice
Low = 0.1 ohm
Mid = 31 ohm
High = 68 ohm
If you just look at numbers then logically speaking you'd think for
Lawton TH900 (25 ohm) it would sound best with the low (0.1 ohm) setting. But to me the mid setting (31 ohm) actually sound the best despite being "wrong". Low (0.1 ohm) just sound too cold/sterile like most solid state amps. High setting (68 ohm) has the best vocal but it start to skew the frequency too much and the rest of the spectrum is unbalanced. So I ended up just leaving it at mid (31 ohm) setting all the time.
I'm pretty sure there is a "sweet spot" somewhere between 20 to 40 ohm output impedance that still work well with 25 ohm headphone.
I couldn't find the measurement number for
Feliks Echo MK2, but I wouldn't be surprised if the output impedance falls somewhere between 20 to 40 ohm.
Another 2 tube amp my friend recommend for Lawton TH900 are:
Shortest Way SW51+
Low = 27 ohm
High = 54 ohm
Hagerman Tuba
Low = 5 ohm
High = 35 ohm
He didn't specifically tell me the setting he used but I'm going to take an educated guess and say for Shortest Way SW51+ it would probably sound good with low setting (27 ohm) and Hagerman Tuba probably at high setting (35 ohm).
If we go by the 1/8 rule, then 25 ohm / 8 = 3.125 ohm. Meaning anything higher than 3.125 ohm output impedance will impart coloration to my Lawton TH900.
Though not saying 0.1 ohm is always bad, my Lyr 3 is 0.1 ohm and it sounds great. Just..... I guess you never know until you physically try it.
Anyway I've rambling on for too long LOL. Also maybe not apples to apples because my amps are hybrid amps. What I'm trying to say is,
I only found out I like this because I tried. If I just follow numbers I'd never discover this.
Cheers!