WinterSnowfall: ...Of course at some point your speakers will need an analogue signal to play back sound....
This does not have to be completely true, considering Class D Amplifier (low pass filter at the does not change principle).
Zimerius: is there any point in using a dedicated audio sound card if you choose to use usb?
It seems to me, that so far nobody mention, that important is what you really hear... some people can distinguish between MP3 320 kbps and lossless FLAC, some not between 128 kbps MP3 and FLAC. So it is good to make some personal listening tests first.
Secondly if you would hear well enough, than you must consider quality of your recordings, complete audio path and maybe if you would "hear as a bat", than even ASIO driver with audio player which supports it (but it comes with a price!!!).
On the other hand there are some "audiophile" accessory, which is expensive, but does not have any impact on sound quality as special oxygen free cables etc. With audio it is as with anything else, if you are interested you would have to study and test it yourself to get best experience.