I'm not technically knowledgeable about computer audio, so I'd like some help understanding why Reference Recordings recommends the use of a sound card in the playback equipment (BTW, I own a number of RR CDs and am glad it is back in business).
From what I know, the original sound cards were an all-in-one device that first converted the digital data from the hard drive to SPDIF and then converted the SPDIF to analog. It may have even amplified the signal after the final conversion. The sound card also took the SPDIF feed from the CD-ROM and converted it to analog. The net result was that speakers were the only sound equipment external to the computer needed for playback.
Audiophiles rejected these sound cards in favor of external conversion devices because (1) the noisy electronic environment inside the computer created distortion, (2) sound cards were cheap devices made to a price point to sell as part of the computer package and (3) sound cards limited the type of sound produced and external DACs did not. As I understand it, quality computer audio systems bypass the sound card for conversion to SPDIF (and therefore for conversion to analog too) by taking the digital feed from the hard drive outside the computer. If this is so, why is it necessary to use a high quality sound card or any sound card at all? Does the sound card perform some other functions that require very high quality parts or sophisticated design? Or does the Berkeley Design Alpha DAC perform only the conversion to analog, leaving the conversion to SPDIF to the Lynx AES? If so, why not substitute a good quality USB DAC for the Berkeley?