The first question might kind sound of dumb, but can the 8bit DAC's on the GBA playback a 16bit audio file? How does the GBA load direct sound waveforms? I was able to get a 16 audio file that is 644kb to run in a GBA game! I assume at this point that samples are loaded directly from the cartridge instead of loading everything into ram as that would have made the game crash. I tested this because of how the DS seems like a step backwards in terms of how it has to load audio files into ram which causes a limit as to how long each sound can be.