The amplifier only amplifies and a good sound card can of course also sound better. I have installed the Asus Xonar Essence STX (still the first version) and find it better than with an amplifier. I was able to compare it with the DT770 Pro from Beyedynamics at a colleague's who uses his mixer via the jack plug on a MacBook.
With the sound card, I found the details extraordinarily crass. Until then I was only used to 20.- headphones and MP3 320kbit and now I also enjoy certain details in the sound when gaming. I recommend that you simply test it when you have the chance so that you can hear for yourself whether you notice a difference.

Hello SvenDiletti,

It's really a question of budget here. Do you already own any speakers or headsets/headphones?

Sound card only, for connection to speakers you need an additional amplifier.