GBA uses a 2 channel DPCM output and it since there's no dedicated sound chip has to do it all via software and from the main CPU (and the secondary.) This restricts most games to having lower 8-11khz audio samples and simple melody as to not screw up the game itself and limit it. SNES used a dedicated chip that output at 33khz (nearly CD) and used 8bit samples over a 16bit chip(or was it the other way around I forget.)

SNES ports though can come VERY close, FF6 most recently is a great case for it as while some sfx are crappier and a few tunes are dulled down, some actually sound superior including the big opera (aria) scene.