I don't know how the JagCD implements CDDA mixing, or if the JagSD was planned to support CDDA on CD images?
If it was/does then I can imagine some interesting homebrew/patches if it was explained to Jag Scene exactly how it works?
I don't know if you followed the AtariSTe scene but a few years ago Pera Putnik did patches to several STe titles to add "CDDA" (or rather downsampled versions of CDDA) being played instead of the normal soundtrack over STe DMA sound.
http://www.atari-forum.com/viewtopic.php?t=27444
http://atari.8bitchip.info/SCRSH/cannonf.html
I can think of 3 native Jaguar cartrige games where CDDA exists on other platforms : Cannon Fodder, Tempest 2000, Zool 2 and I am sure there are more.
If they could be patched to play CDDA tracks instead of music, I can imagine that being cool don't you?
I don't know much about the AtariST->Jaguar ports but there are CDDA tracks for ST games on other platforms out there (e.g. Amiga CD32)
http://eab.abime.net/showthread.php?t=26552