Check out the LINKS BELOW FOR SOMETHING CALLED A USB DAC.
Or an external sound card. I have a cheap external sound card and it works fine.
External is key because of the electronic hash zipping around in your typical computer.
As for the distance I gave up, parked my computer next to my system, use my main monitor for viewing my desktop, and wireless mouse and keyboard for control.
If you want to keep em seperate maybe a 12' USB cable will work, or 12" audio cables,
havent tried either one


http://www.audio-magus.com/


http://www.firestone-audio.com/