Hello. Sorry if I am a bit late in to the conversation. I do have a few questions so I can help you.
1. What are your priorities? Absolute best sound for the buck or a more immersive experience?
If you already have speakers, you know how much better for naturally recreating movies they are. Movies, to simply put it, are made in mind to be played through speakers. So, if movies are the focus, get speakers. I recommend AudioEngine 2 speakers. Great dynamic range, very deep, tight and accurate bass, and, most importantly for gaming, excellent sound staging, are properties of these speakers. At $200, they are a superb bargain for what you get.
Just a quick side note-if you do really want a 5.1 system that sounds good, do NOT buy
A. A "gaming" set of speakers-these are such absolute crap I don't know how they sell them (Yes, I have heard many, many systems at friends' houses, they all are s*** compared to mine)
B. A 5.1 setup that comes in a box-once again, same thing. People think their systems are great because they don't know any better. I do not mean to be offensive at all-it's not people's fault. I bought a "sample" system (well, I have a sample headphone and speaker setup) just to show my friends how they could get better for less. Almost all of em who have heard one of the setups either bought a similar speaker or headphone setup. If you are willing to go beyond Bose, Creative, etc. for speakers, or Bose, Razr, Beats, for headphones, I can get you to audio nirvana.
If you spring for the AudioEngines, you will NOT need to upgrade your sound card. Sure, if you want to ever so slightly increase your sound quality, then you can buy a DAC (Digital to Analogue Converter, which either connects to your computer via either USB or Coaxial/Optical and completely bypasses your internal sound card. If you
Sorry for my rant. Back to your question.
2. Have you considered headphones?
It is a known fact that headphones can recreate the greatest tonal accuracy and soundstaging for the price. Just letting you know that there are no really great soundingn headphones out there with a mic. If you cannot live without a mic and quality is not the top concern, get the Corsair Vengeance 2000. But I would recommend the Audio-Technica ATH-AD700. Hands down best gaming and movie performance for the price. Oh yeah, it also ROCKS with any music you throw at it. At $138 on Amazon...well...it's a friggen amazing deal. For optimal sound quality (It won't sound it's best coming straight from your computer) pair it with the Fiio E10, a headphone amp and DAC which will greatly enhance and optimize your headphone listening experience. Now at only $65.99 from B&H...wow. So for $203.99, you can get a headphone setup that will blow all of your friends crap away. This setup wrecks my Beats Pros ($450) in all respects.
Just my $0.02
Good luck! I'll check back on this thread later.