I think the NeoGeoCD system doesn't load audio tracks properly. I've focused on the game Metal Slug (World) and WindJammers (World) in cue + img (truerip) format. After setting the correct bios, the game loads correctly, but when it comes to playing the music doesn't do it correctly. With IsoBuster, I changed the format from cue + img to bin + cue and iso + cue. In all cases, it does the same thing: it loads the game well, but not the music tracks.
To rule out misconfiguration problems on my part, I downloaded retroarch 1.7.6 for Windows with free fba core. In this scenario, (same rom and same bios as with rpi3) I can load the game and the music works perfectly.
Have you been able to make the audio tracks sound correctly with NeoGeo CD? Am I missing anything?
Rpi3 without overclock
8bitdo SF30 Pro
BIOS used: neogeo.zip and neocdz.zip in the neogeocd folder.