Everything below I own or owned at some point. Anything "popular" that is gaming related, I have pretty much tested/returned the crap and dismissed, minus a few exceptions. I am also assuming just gaming, and not music. You want a sound card if you game man. Especially FPS's. Relying on in game positioning and Dolby really is a disadvantage at times. If FPS's aren't your thing...There are great DAC/Amps/Headphone combos. Too many to list really. But if you want that route, just reply.
Start small and go for bang for the buck. For the love of god avoid Bose, Beats and Razer. Avoid USB headsets period. Avoid USB anything for sound and games unless you are going to go the full gambit and do it correctly.
Just get this sound card. It's the best bang for the buck right now:
Creative Sound Blaster Zx PCIe Gaming Sound Card with High Performance Headphone Amp and Desktop Audio Control Module at Amazon.com
Your headphones for gaming should always be open unless there is a reason for you to have closed headphones (Better sound-stages generally). It's tough to beat the HD558's cost/quality ratio. They are light on bass, but it's there:
Amazon.com: Sennheiser HD 558 Headphones: Electronics
If you MUST have closed back get the A700X's:
Amazon.com: Audio Technica ATH-A700X Headphones: Electronics
Your mic will be an Antlion:
AntLion Audio AntLion Audio
These three items will give you better sound quality for gaming than any gaming headset out there under 300 bucks. Much better.
As far as headsets go... For quality, you will want to spend around 400 bucks. Anything less I have found is pretty much cheaply made, bad sound quality junk.
The Sennheiser Game One. Lacks thumping bass, but it's there. The sound quality is the HD558's:
Amazon.com: Sennheiser G4ME ONE PC Gaming Headset, White: Electronics
If you want a closed back headset go with the MMX 300:
Amazon.com: Beyerdynamic MMX300 PC Gaming Premium Digital Headset with Microphone: Electronics
General rule of thumb and there is no science here, just experience . You do NOT need an amp until you start hitting headphones that cost about 350 bucks.
Hope this helps.