Well you have to take this on a case by case basis. It depends on how you implement this. The general answer is yes, a computer can replace a really good transport in two ways. First, it can send files to a dedicated music server device like a Squeezebox or Transporter. I use a Squeezebox with a dCS Delius+Purcell and get some pretty astounding results for the price. The SPDIF/COAX output on the Squeezebox is good enough to rival some really heavy duty CD turntables.
The second way you can do it is to use a DAC that accepts USB. This is quickly becoming the preferred method. The catch is that not all USB DACs do it right. A technical person I know who was at CES said the big thing this year is USB done right (asynchronous), with companies like dCS, Ayre, and PS Audio all coming out with solutions over the next year. Ayre, for example, is coming out with a USB DAC for under or around $2,000. What seems to be happening is that the companies that figured out how to do USB the right way are now licensing their technology so more devices are coming out. If I understand correctly, properly implemented USB has the potential to be better than SPDIF (less jitter, better clocking?). This is probably most likely what will replace the dedicated CD transport in the high-end over the next few years.
With this method, you use a small computer or laptop to play the music files, organize your library and output the files to the DAC via USB. A quiet laptop would suffice and the device you use to play the files should have little or no impact on the sound.
Another thing that important is how you actually rip the files to your hard drive. You will want to at least use the error correction option or preferably a dedicated program like (Exact Audio Copy) EAC to rip the files in a secure mode to correct any errors on the disc to get as perfect a rip as possible. You will also want to store the files in a lossless format like .FLAC or .ALAC or preferably an uncompressed format like .WAV or .AIFF.
You should be able to get results equal to if not better than some of the best CD transports for a fraction of the price. Your best bet will probably be the new Ayre DAC but it isn't out yet.
The second way you can do it is to use a DAC that accepts USB. This is quickly becoming the preferred method. The catch is that not all USB DACs do it right. A technical person I know who was at CES said the big thing this year is USB done right (asynchronous), with companies like dCS, Ayre, and PS Audio all coming out with solutions over the next year. Ayre, for example, is coming out with a USB DAC for under or around $2,000. What seems to be happening is that the companies that figured out how to do USB the right way are now licensing their technology so more devices are coming out. If I understand correctly, properly implemented USB has the potential to be better than SPDIF (less jitter, better clocking?). This is probably most likely what will replace the dedicated CD transport in the high-end over the next few years.
With this method, you use a small computer or laptop to play the music files, organize your library and output the files to the DAC via USB. A quiet laptop would suffice and the device you use to play the files should have little or no impact on the sound.
Another thing that important is how you actually rip the files to your hard drive. You will want to at least use the error correction option or preferably a dedicated program like (Exact Audio Copy) EAC to rip the files in a secure mode to correct any errors on the disc to get as perfect a rip as possible. You will also want to store the files in a lossless format like .FLAC or .ALAC or preferably an uncompressed format like .WAV or .AIFF.
You should be able to get results equal to if not better than some of the best CD transports for a fraction of the price. Your best bet will probably be the new Ayre DAC but it isn't out yet.