a few questions..
what size speakers do you need/want?
-satelites (good for small rooms, lack bass impact, are easy to hide and small)
-bookshelves (good for medium rooms, more bass impact, not so easy to hide but well rounded)
-floorstanders (good for medium or large rooms, significant bass impact, very large and conspicuous but powerfull)
-subwoofer (required for bass impact on satelite systems, optional on bookshelf or floorstander systems but does add more low end)
will you have more than one source?
-will you just be using the computer or will you need to add lets say a video game system, mp3 player, internet radio or other such alternate source to them?
-if yes do you need them to be hooked up at the same time or is swapping cables okay?
digital or analog sources?
-how will you be connecting? via hdmi, optical or 3.5mm?
-do you have a pc soundcard? list it
-do you have a video card? list it
-is using hdmi through a receiver to your tv or monitors okay with you or would you prefer not?
distance from pc?
-at a desk or do you sit back on a couch or chair?
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generally a receiver is good if you have multiple sources and want to swap between them. they might not have the absolute best in class DAC or amps but generally good enough. receivers are also fairly priced and will run less than seperates.
if you already have a good soundcard to act as a DAC then you can use just an amplifier. this means more money put into speakers.
if you do not then you can get an external dac and also an amplifier to power speakers. however, between an amp and dac this could eat up half of your budget easy.
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i personally use a receiver in my own setup (link on top right in my sig) which is a 5.1 satelite system using klispch speakers and a pioneer receiver. i use multiple input devices which makes it very convenient for me.