Dagar, K.A.R.R - thanks for doing this back-tracking and reporting this issue.
Around this time last year, I transitioned the CDDA work from subversion (layered on top of DOSBox's SVN sources) to git, at which point bugs and enhancements continued publicly on GitHub.
This Monkey Island audio issue was reported in May, https://github.com/dosbox-staging/dosbox-staging/issues/385 and fixed in this pull request: https://github.com/dosbox-staging/dosbox-staging/pull/387. There have been more improvements since then. This isn't a promotion of git or that project and I'm only mentioning it to point to the status of the work.
Yesterplay80 and I both would like ECE using the the most update-to-date CDDA code. I've offered to generate a diff, however I haven't figured out how to separate other dosbox-staging changes from the CDDA-specific changes.
If someone wants to pick this up , the CDDA code is relatively self-contained (src/lib/decoders/*, src/dos/cdrom_image.cpp, src/dos/cdrom.h).
It might (or should) be possible to take the ECE code-base, and then try layering (overwriting) the older CDDA sources with the latest files from the git master branch. If someone wants to try this, I would be happy to help via PM.