Yes.
"Improvements" in audio do to internal sound cards are usually do to the placebo effect. That's not the same for EXternal soundcards though, thats key, keep that in mind.
What external DACs do is they convert the binary file that you want to view into an analog signal. A motherboard has this, but it is typically very bad.
The DAC makes your audio sound better by getting the DAC away from the computer noise, and also using an overall higher quality DAC which converts the audio more efficiently and cleanly. An AMP is optional since it just amplifies the signal.
They are kind of expensive though, but you get what your paid for unlike a sound card.
If you want to get what a sound card does, just download EQing software and make your own audio profile (more bass, mids, highs, etc.)