The circuit is more like the srm-001 blown up by a bunch. So opamps input, solid state version of grounded grid output stage, resistor loaded, and capacitor coupled output. Positively ancient design by any standard. Did not even replace the power resistors with current sources. Saying that the output capacitance is that low because the two devices are in series clearly shows no understanding on how that design works. And the series output inductors are not a great idea either.
The headphones may be decent, I don't know because I have not heard them, but there are so many decent headphone amps out there that buying the hifiman version seems like a waste of money.