Does cmoy amp is better than a soundcard? - Not necessarily.
What is better audio to you, louder or cleaner sound? because they're two different thing. The amp is dependent of what your quality your source be.
Here is a brief explanation about how DAC and Amplifier comes into play. Remember - onboard DAC does convert the digital signal to audio signal inside your computer where it's the noisiest place due to other process being done. While external DAC isolate the conversion of your audio signal where is less noisy. So the process of external DAC is cleaner than the onboard DAC. Then you amplified where your headphone can deliver all the sound your DAC has process.
There's a reason why I would recommend the Aune T1 MK2 DAC+Amp, because you can change the tube and find the sound quality to your liking. So read more about it and don't just take my words from it and you'll be surprise what other users think about it too.
One thing I can say about all this is if you started a system that you think it's the great, an absolute best. Stop there and don't try to compare it anymore, because if you do, you will open pandoras box. And if you are curious about it though then read it first and educate yourself from the net what's DAC and amplifiers can do, and why other units are differently priced.
So before you start to wonder off about sound quality, bring your favorite tune and ask the sales person if you can listen to it on the products they have. Bring someone with you to compare what you hearing and what they're hearing. You will notice that both of you may actually NOT hearing the same from the same system. And that you're the only person who will think that it's sound excellent. If someone happened to hear the same thing you hear then it's wonderful. Remember, it's all what you want to hear not what we want to hear.