As far as I can tell, these "Digital Audio Discs" are actually DVD Video discs that contain high-res PCM audio tracks.
This was an alternative to DVD Audio discs, which are a separate format that uses MLP encoding.
If these are just DVDs, this is my process for ripping them (or Blu-rays) to separate audio tracks.
1.
Rip the disc using MakeMKV. This creates a single .MKV file containing the tracks that you select.
It can optionally encode PCM audio to FLAC if you select the "FLAC" profile.
2.
Use MKVToolNix GUI to strip out the video track, and create separate MKA audio tracks from the MKV file.To do this, drag the MKV file to the "source files" list, and only select the audio track that you want in the MKA files.
On the output tab, set
MKVToolNix GUI to split the file based on all chapters.
Hit "start multiplexing" to run this, and you will get tracks named: "Album-001.mka" etc.
You can import these to your Media Center library and it will play them directly.
If you want another audio format such as FLAC, you can use Media Center to convert from MKA to FLAC.
This method works for all DVD audio tracks, if you want to rip the 5.1 DTS track losslessly for example (note: do not convert formats such as DTS or AC3 to FLAC).