the example i like to use is that you can usually taste the difference between a $300 steak vs a $200 steak. However, adding $100 of seasoning onto a $200 steak doesn't make any sense as the $300 steak will always taste better than the $200 steak no matter how much seasoning you add to the cheaper steak.
amp/DAC are just seasoning for headphones. they can improve the sound quality by maybe 10-25%, but headphones+source is always the primary factor that depends your sound quality. your money goes farther if you put it into a better pair of headphones.
No the Dac and amp are not seasonings, the Amp and Dac are like the cooking methods for your headphones,
The Dac and amp supply the raw signals that allow your headphone to play music, going to steak. Would you rather have a $200 steak cooked on a $100 grill or a $300 steak cooked in a $20 mircowave... I'll tell you now mircowave steaks is terrible
if anything Equalizers are like teh seasonings of Audio. Take a good EQ and you can make a $100 headphone sound really epic! But that's assuming you running it through a good dac and amp. No matter what you do mircowave steaks tastes BAD.