I am curious to the result
a GBA SP without backlit
Mind that the light has an effect on the sound of the SP
...if an improvement in sound ultimately cannot be made, then internalising the jack is merely cosmetic...
the adapters do not fit as solidly as a mini-jack, so, an easy mod does have a use I think, with or without an extreme improvement on the sound
the drumkit i used on LSDJ,
SPs are known to have problems with sample playback, I would not take that output as a quality control. Maybe try nanoloop...