No Microcontroller Used
There is no microcontroller in the amp. The larger chip is a volume/balance control chip that is commanded up/down by grounding a pin. There is 2dB volume change per click and is slews quickly if held down. The balance feature is not used and the chip always starts in balanced mode.
The amplifier has adjustable gain and an internal charge pump so it generates its own negative voltage so the output has zero DC offset and no large capacitors are needed on the output to keep things small. Both chips are made by Maxim.