I don't consider myself an Audiophile but I did do a lot of research for my home entertainment center. I have a set of Cambridge Soundworks 5.1 spearkers setup for my computer which I have enjoyed but I payed a little more for my home theater.
The first thing is that the amp/reciever is everything. You have to hear it to decided what you like. The sound is based on how the amplifier is tuned. Some amps give you low noise, some give you high gain, etc. Denon and Yamaha have some really good high end equipment. As a musician I tend to like the Rotel equipment. Its a British make but they don't filter out a lot of the noise. This will let you hear some of the more intricate details in music. But for games its all flat anyway so you might not even need that. The Rotel reciever was around 1k and the Denon and Yamaha, with slight differences in sound are around 800-900.
For speakers, once again, you have to listen to them, but I got Klipsch Reference speakers: 2 floor spears, a center channel and 2 surrounds. They sound great and are very efficient speakers, meaning I can get more sound for less power. The entire Reference line is great, its just a matter of how much power you want to put out.
For a subwoofer, I got a Velodyne sub. They make a standard emag driven sub and a servo driven sub. I got the servo driven sub. Its a lot crisper and with the dampening system on it, you get no excess ring. And for a 10inch sub it out powers most subs double its size. Very nice toy. That was about 1k.
Now for listening to music, either get an amazing sound card or get a seperate DVD player. Most of the ones they sell in bestbuy and what not will distort the sound enough that at high volumes you can pick out the artifacts. I went with Rotel and I love it.
My whole surround setup was 7k. Pretty cheap on the full scale of things. The next step up in the setup would take me to around 20k. So this isn't the top of the line but it does put out a very nice sound. However, if you can't really hear the difference just go with one of the box sets from Bestbuy, they are cheaper and match the quality of the sound putout from a standard sound card.
The key however, is to listen to the parts. Its all personal choice. No point in paying an extra 5k when you can't hear the difference.