Nowadays for headphones and active speakers internal soundcards provide the near same audio quality as any dac+amp. Of course, the audiophiles wont wanna hear this...shhhh...lets keep this a secret.
However i still use a dac+amp as thats what i have had for years and a soundcard wont fit in my case. but anything over 500-1000budget for the dac/amp and you start to hit the law of diminishing returns big time. These fools pay 2grand and think it makes a difference, but its all subjective claims that are so unsound its hilarious. Most honest objective clear minded unbiased audiophile and/or audio engineers will tell you there is no discernible difference between 500bucks and 1-2000, tech nowadays has caught up, lota irrational snake oil out there. What these audiophiles cant understand is concepts like how our ears get fatigued in very short time and this alone can mean you stand no chance of hearing any differences. Same goes for headphones, there is a very slight diff between a mid range and high end. The price is no indication of sound quality.
The best gaming setup is largely subjective. Big screens block the imaging with two front stereo speakers. Big subwoofers require serious base traps and dampening. Large rooms require bigger sized speakers.
Im old school, for my room I just use two high quality studio active powered monitors, make sure the tweets are at your ear height and the imaging/separating is right (~1.5M apart???), without imaging it sucks.
Game design is key, when I first heard crysis 2 I was blown away by the quality of the sounds.
You can go down the rabbit hole with speakers, its truly irrational pricing, big rooms get so expensive so here best to set a practical budget, dont be fooled by the audiophile talk. Just assume once over a few grand they all sound the same.
As far as headphones, stick with open dynamics as they are the most affordable, can be ran off anything even a laptop and are best bang for buck. Planar magnetics are too expensive and require expensive gear to run, but have a more clinical sound.
The two best open dynamics by far are Sennhieser HD600 & HD800 S.
The 800s are the most comfy over ear headphones you will get and have the most perceived soundstage, they are very analytical and revealing but surprisingly work so well in anything you throw at them. They are the gold standard period. The 600s are fatiguing on the ears after just a few hours but have a unique sound of their own, the 600s are special to me as they were my first real headphones are they represented such good value for money and until the 800 came out were the gold standard.
Beyedynamics dt1990 pro are amazing build quality for their price but have a harsh treble and are more generic studio quality. But they are more comfy than the 600s.
Be warned though!!! You ears get fatigued quickly thanks to how loud everything today is.
So look for a Chinese brand dac and amp, separate for headphones too. If you go one unit you will have to toggle the output between active speakers and headphones.
But I use my HD800s straight out of the laptop jack (too lazy to get the dac/amp out) and dam...they sound effn good.