Buy and sell used

It doesn’t affect dynamic range on the normal and quiet normalization settings.

RCA cables

If you have an iPhone with lightning port you might need some kind of cable to get digital output

Find something else to focus on while listening like a simple game without audio

You can use any official apple or beats earphones to find out the listening volume in the health app. It’ll give you an idea of what a safe volume sounds like and then you can listen at that loudness on your other headphones

If you mean your hair you gotta change your hairstyle

Custom molded silicone tips?

ADV Sound

1990 had the sharpest imaging I’ve ever heard. The center image is so sharp and definite. The treble is pronounced but never bothered me ymmv. Separation and resolving ability were good, no veil at all. To me the bass was quite strong, but honestly none of the headphones you’re looking at will have super thick bass without EQ.

Assuming it is low enough (<1%) it will never matter more than pretty much anything else in your listening environment like ambient noise, psychoacoustics, mood, volume level, recording quality, the precise position of the headphones on your head, a thousand other things. It doesn’t really make sense to compare such tiny metrics when you’re talking about something so subjective like audio. I can bet you’ll never hear the difference between 1% and 0.1% THD

Is it the glasses frames squeaking against the pads? There isn’t much you can do. Maybe try glasses with thinner temples and metal material.

As in literally having enough power to produce enough volume yes you’re good. Will you get better sound with a crazy expensive amp maybe I don’t know

Buy used

There is zero chance you know your preferences without actually listening to any headphones. What are you using now? What do you like/not like about them?

Put the Koss on a headband and you’ll regret the Aurvana even more

When are you hearing bass in one side only? When you game or in music?

I think garbage is a bit strong… I do agree it’s a little shouty so I lower it by 2-3db but the bass is definitely not overdone. IMO the tuning is especially good for low volume listening.

Waste of money

You mention timing differences between left and right to contribute to sound localization, which is true, but what does that have to do with headphones?