And the AMP is only responsible for powering/giving electricity to the headphones/speakers? So the pre-amp is the only component that matters in sound quality, And the amp is responsoble only to the volume?
(Btw i know that the DAC also affects sound, But i am talking about amps of course)

Well, ideally, they both should be low in distortion and good in sound quality, but the power amp is usually what you look to for how many Watts you can push to a certain load. Preamps just prepare the signal for the power amp - both can have a sizeable effect. I have a tube preamp that I hook up sometimes, it adds some fun color to the sound. But I could also hook up my DAC/pre to a tube power amp and get the 'tube sound' from the power section. You just play around with combos until your ears and wallet are happy .