I second the recommendation to look for used equipment. Since you're going 2-channel, a receiver is unnecessary, a low end integrated amp can be had for $200-400 and would be better sounding than pretty much any receiver. I don't use speakers, so I can't make any comments on what to look for there.
No matter which direction you go, however, you will be source limited. Neither .ogg files nor any x-fi/audigy card will do justice to a decent integrated amp and speakers.
With your source, I would look at audio asylum's forums. They have an immense amount of information on vintage receivers, which will generally outperform anything in the price range you are looking at. Most of them retailed for $200-500 in the 70's and 80's and are available on ebay for $30-100. High end Amplification has changed very little in the last 20 years, so you're really just looking for the cleanest output you can find.
Speakers are much more difficult. The best way to choose would be to hook them up with whatever amplification and source you will use and then play a wide variety of music. Its similar to how you would choose headphones, but the differences will be much smaller between pairs of speakers than with pairs of headphones.
If you were to ever move to a higher budget, headroom has absolutely wonderful headphone amps which can be configured to act as both a high end dac and preamp, effectively removing the x-fi from your music setup and leaving you with a wide variety of choices for amplification.