you should consider comapre the porthphile 627x against the rsa lighting
check it out
I have used the expensive OPA627BP nine years ago in my XP-7 in conjunction with BUF634 & offered it 10 years ago with my first amp the HR-2 as an option. It is a great chip but it has high input noise which I won't recommend it in now a days portable amp that are designed for IEMs.
I read both of the links but I see no mention of the F-35, the lightning, which has some of the best lowest input noise op-amps that work great with IEMs. Also the lightning can swing in balanced around 32 volts p-p which is well needed to drive hard Ortho phones.