The GBA has the same structure for all instruments as long as the m4a engine is used.
In this article, we will explain how to port DirectSound.
(Because manual porting of drums and multisamples is difficult)
Select a song that contains orchestral hits and EXPORT it from the instrument data.
Import it into FE8 NIMAP #55.
So I would just have to find a different guide on how to extract the instruments? Or does FEBuilder have this feature similar to how it can transplant music from other games?