Dude if you are a PC gamer you have a wider variety of sound substitutes and enhancements, as for console gaming not much except for the amp line such as astros and sounblasters. So lets get started in CS: GO I utilized my setup which was sound from a pair of headphones and a soundcard. To be honest it is better to stick to a soundcard if you are on PC because it is insanely accurate as opposed to an external source but remember external sources such as the Recon 3D, Creative X7, Asus Xonar, Mixamp Pro and Other amps/dacs are pretty beast. The thing you should worry about is getting a pair of Headphones or a Headset. I recommend getting Headphones or a Headset which are not marketed towards Gaming because Gaming Headsets and Headphones are pure BS and are bassy as hell. In CS: GO You want to hear people using the Silenced Weapons like the M4A1S or Loud Weapons such as the AWP so my opinion as well as many others on this website agree that Audio-technica, Sennheiser, AKG, and Beyerdynamic make some Insanely beast headphones due to their accuracy and sounstages. So final point is, GET A HEADPHONE FROM THIS BRANDS I RECOMMENDED AND USE A MOD MIC WITH IT FOR CHAT, GET A SOUNDCARD RATHER THAN AN AMP/DAC, AND LASTLY GO BEAST MODE. Good Luck man and have fun.
I personally recommend the Audio-Technica AD700 (If you cant find it go with the AD700x), AKG k701 or k702, these cans do wonders for competitive gaming when paired with a powergul sound card.