I searched some information on GBA sound chips on internet... It is a combination of a stereo PCM voice with 4 synthesized voices. Synthesize voice 1,2 are square waves with variable pulse width, voice 3 is a very primitive wavetable voice, voice 4 is a noise generator. That sound pretty reasonable but wait, there is NO ENVELOPE GENERATOR. (It is a shame that the Commodore 64 is still state of the art technology regarding sound synthesis.)

IMO the synthesizer is simple enough to be driven directly by the programmers. Any programmer can put a sound frequency in a register and start the note. Just document the registers and make them available in a unit.

Due to the lack of volume envelopes the musical abilities of the synthesizer are limited, so the stereo PCM sound voice looks much more promising. However, writing a module player for the GBA at this time looks too optimistic.

I think it is the most realistic to expect games to use the synthesizer for music and the PCM for sound effects.