Nice work if your able to do it.
Did you get inspiration from anywhere to do all this or are you just more technically savvy than us mere mortal diy'ers.
It just proves a point that a standard headphone put socket is usually compromised by cheaper components and that even when spending on a headphone amp cost ccutting can hold back the results.
From what I've read and from others who tweak MF cans, MF argue the case that the components don't matter. But it's more like they would not sell as many for the extra price of including quality components. An extra few quid at manufacture time gets grossly inflated at the shop price end.
Any way this is a nice post and I'm glad that you have the knowledge and impetus to improve it.
Sexy cables next then...
Steve