You can also just get a USB/Firewire device to get either a digital or optical out of your computer and then line that into an external DAC component (probably better quality and cost than an integrated computer usb/dac device).
Also you can just buy an Airport Express and get the optical out cable to go into a DAC, this way the computer does not even need to be near the stereo. The Mini will be the best price and can come with an 80GB drive you can swap or add to ...I have all my music lossless so if you plan to compress then going with a cheaper integrated usb/dac might be fine. You can check out my system ...I think it is similar to what you are looking at.
Also you can just buy an Airport Express and get the optical out cable to go into a DAC, this way the computer does not even need to be near the stereo. The Mini will be the best price and can come with an 80GB drive you can swap or add to ...I have all my music lossless so if you plan to compress then going with a cheaper integrated usb/dac might be fine. You can check out my system ...I think it is similar to what you are looking at.