I mean when people think you need an amp to run HD 6X0 series when I reality the whole lineup is easy to drive to deafening levels.

Amps don’t change the sound quality. People saying you need an amp are liars.

Sennheiser IE Pro line has the best behaved cables for me and they’re very soft.

They’re using the balanced port for the calculation so if you’re just using 3.5mm it won’t be accurate at all.

Which headphones? That calculation only works on Apple headphones and beats.

Yes

Don’t worry about impedance. I have the HD 6XX and 660s and there’s no sound quality difference running off my iPhone vs an amp