For adding custom song you need
thememii
https://wiibrew.org/wiki/ThemeMii
BrawlCrate
https://gbatemp.net/download/brawlcrate-v0-39h1.38026/
AudioLoopingConverter
https://gbatemp.net/download/looping-audio-converter-version-3-0.38027/
ectract iplsound.bsar with thememii
Extract and open...
Anbernic's SP clone will be $60 and I think I'll buy it. Looks decent enough and it will stop me from drooling over every single new handheld that comes out.