Ah, well.
Take i.e. "Dune" asm.
You assemble it in emulator to memory
then you can save it from BASIC - SAVE"DUNE.BIN",B,&8000,&51E
In your BASIC-Game you set
MEMORY &7FFF
and
LOAD"dune.bin",&8000
and if you want the music to play: CALL &8000. now it plays "infinite" until you CALL &8003.