Looking to get started with high-resolution computer audio? It's really pretty easy, for less than $100 you can buy an M-Audio Transit to get up to 24bit/96kHz digital audio off your computer via the USB interface, and output Toslink optical digital audio to your digital to analog converter. And boy does 24/96 audio sound!
The thing you've really got to understand is that as of this writing USB drivers for the TAS1020 chip in the Transit and your computer operating system are still a little crude. So you have to change settings in the easy to use M-Audio driver application to match the sample rate of the music being played. In other words, you can't just make a playlist mixing 16/44 tracks from cd rips mixed in with 24/96 music downloads as the computer will resample the high-rez track to whatever is set in the driver. So, at least for the moment, you will have to make separate playlists of high-rez music and manually set the driver to 24/96 in order to get the full benefit. All HeadRoom digital to analog converters accept high-rez audio on their optical input, as do most other currently built commercial DACs. The biggest high-rez music download site is HD Tracks. One of the best places to learn more and stay up to date on this subject is at Chris Connaker's "Computer Audiophile" blog. Check out his page reviewing high-rez download sites and his terrific Computer Audiophile Acadamy section to learn much, much more.