Because we're adaptable creatures, even bad sound will sound fine when you get used to it. If you've been listening to DVD sound through your TV speakers, this system will be a huge improvement. That doesn't mean that it's a good deal. Computer speakers are designed for listening with the listener in front of a keyboard looking at a screen and the speakers close in. Near-field refers to the positioning of the speakers and listener, usually an equilateral triangle. The sound arrives at the listener's ears before it's reflected off any surfaces, thus near-field. I assume THX certified for near-field positioning means that the positioning is such that the near-field requirements are met. If the sound is reflected, then it wouldn't be THX certified.
I'm no expert, but in my opinion, you'd be much better off finding a home theater in a box system from a reputable manufacturer and purchasing that for your living room, than you would be purchasing a sound system designed for computers. The other option is to purchase inexpensive components, AV receiver, sub and speakers, and replace them piecemeal as you adapt to better sound with experience.
