You just saved my day! Although I don't know if I should be that happy - apparently, the issue is in my laptop. Tested them on another and they sound great! Thank you! (Now let's see if this sound card can even be fixed/changed.) Edit: Reinstalled drivers. It's fixed now. I feel stupid.

My headphones finally arrived - MH755 (modded by me) and MH750. I don't know, but after reading how much praise they receive online I have the feeling that mine are not genuine. In the Frequency Response section here ( https://www.audiocheck.net/soundtests_headphones.php ) I can't hear anything...