The intro and end music are available as MP3s on the root of my BARIS CD (it's an original, not a burned copy). I expect the game doesn't make use of them but that they were put there as "extras" of some sort.
*Forrages for BARIS CD* - Nope, I see none on my original (re-release) white label disc. However, if I stick it in a CD player, i can hear the music, showing that there is CD-audio on the disc.
Re. the analog CD audio, I get sound and music during the game--just not the intro or end music.
Yes, this will be because the sound during the game is encoded, and so is passed through IDE to the soundcard, where it is converted to the waveform we hear. The difference is that the music is stored on the CD as a waveform itself, and is decoded not at the sound card, but at the CD-ROM, and will pass through the small 4-pin wire to the soundcard, which merely passes it through to the speakers. So, if this 4-pin wire is not connected, you may not hear the CD audio.