On headphones I'm probably much like rontonomo. I prefer brands who focus on headphones rather than gaming brands. Sennheiser HD 518 and HD 650 are two wide soundstage headphones with excellent sound. One at around $100 and the other is around $300 now, I think. They're open back, so if your PC or where you live is a bit noisy they're maybe not the best option. You can combine that with Window 10's virtual spatial sound processing to get a 3D effect if you want that. If your budget is bigger and you like something that shuts out ambient noise I noticed that Sennheiser is launching a closed back headphone that is supposed to maintain the sound signature of an open back one, called HD 820. Those will retail at 2,500 bucks and they won't be out until the summer. There are other brands, like the Focal Clear that supposedly are some of the better sounding headphones around. Those will set you back a nifty $1,500. You'll also need a good external headphone amp to get the best out of more expensive headphones. My own setup is an Asus Xonar DSX sound card connected to a little external headphone tube amp. And then you'll obviously have to get some sort of condenser mic to get your voice back into the game.
Anyhoo, like you see. It's easy to make things extremely expensive really fast on sound. Those examples aren't even the most expensive you can find.
Expanding on the speaker part... I am personally eyeing a pair of speakers called Monkey Banana Gibbon 5. They're supposedly quite excellent at a "decent" price, around 170 euros a piece. They're 5" active monitor speakers, allowing them to connect to a sound card like the Xonar DSX. Personally, I'm just looking at a 2.0 or 2.1 setup, but the speaker type can obviously be bought at any number you like.
Their subwoofer is quite expensive, so for me that would have to wait for a month or so.