The biggest problem with my HF580 was the annoying 700 hz bump and I flattened it with damping material
behind the driver in combination with the use of the extra set of light grey fabric earpads like you received with the headphone.
The sheepskin earpads was not the solution, I ordered them since many of you are so enthusiastic about them. But if your headphone drivers behave like mine (I guess they are), just forget this: you are choking it with those earpads. Putting a lot of damping and distance between the drivers and your ears is just not the solution if you ask me. And don't start talking about how wonderful it raises the bass frequencies; yes it does raise them, but if you need that, you will not have the right amplifier for those headphones.
Perhaps the Aiva earpads or something similar might be a good choice, I ordered some nameless ones that does the job for me.
Then when it is bulky waste day (in my country that's once a week) unzip or cut open a used mattrass and cut out a piece of clean memory foam. You will like the result when you do the same thing as described here (scroll a bit down):
https://www.headphonesty.com/2020/08/review-takstar-hf-580/
You don't need the round memory foam thing from Grado as that guy uses (not that you cannot make them yourself, but it's not that easy), just get your foam and cut a piece of about 3 - 4 cms (height; I used 33 mms as it was was the thickness of the sheet in the mattrass) times the length (about the circumference at the inside) with a thickness of about 1,5 cms. Thicker means more damping and thinner means less. Just listen for a while what has you preference. Oh and please verify that both pieces of foam that you cut have the exact same measurements and are both installed exactly the same way. If you don't, you will sooner or later notice an annoying difference between the right and left side of your headphone.
You might do a cable mod too while you're busy. This in order to use them balanced, as they need power to sound good; in case you go for a 3,5 mm jack be aware to buy some decent female adapters for your headphones, so that you're sure of a solid contact now and later.
For measurements please have a look in the link.
Fyi I payed €137 for the headphone and some 3 or 4 euros for the jacks. I own Sennh. HD580, HD650, AKG K701, Grado SR60 and SR80x. Except for the HD650, imo these are all headphones not worthy of buying without tweaking (Hd580 a bit shrill, K701 not enough bass, SR60 lifeless and SR80x too much midrange forward.
The mod for the Takstar is relatively easy and (after the mod) has perhaps the best value for money out of these headphones. Also in absolute terms it is a good headphone with this mod.