For this post however, I'll keep it brief and simple as to not bury the important pieces of information in a long post that not everyone might read.
Long story short, if your GPD XD+ shows speaker / headphone issues after flashing the latest CleanROM, please flash the file attached to this post on top of it.
The easiest way, if you are freshly migrating to CleanROM, is to just replace the boot.img file inside the CleanROM folder with the one from the link below prior to flashing.
This fix will however revert you to stock 1.8GHz clock speeds, instead of the 2.1GHz CleanROM usually provides.
Important note: older XD+ models should stay away from this fix as the speaker / headphone fix is exclusive to the new XD+ VR model, flashing this fix on older XD+ models will actually introduce this very same issue, as the headphone jack configurations won't match the hardware!
This fix is something that should only be flashed if you have speaker / headphone issues!