Shortly after Amazon announced the Echo Dot 2, I wondered if it could be hacked to add S/PDIF output so I ordered one. I received it yesterday and started reverse engineering it.
There's certainly more to it than I expected. Just the mechanical design appears very sophisticated, including a cast aluminum CPU heatsink and a rubber seal to prevent feedback.
The motherboard has been completely redesigned since the first generation, replacing the TI CPU with a Mediatek MT8163V, specs similar to the Raspberry Pi 3. There's a chip marked KMFJ20005A that is obviously a memory chip, but even the capacity seems to be elusive to online searching. The RF transceiver is a MT6625L. What's odd is that based on the datasheet I could find, it seems to have a shared IF path for the Bluetooth and 5GHz Wifi. Maybe there are more shared blocks in the chip than what the block diagram would imply? There's a MT6323 mixed signal chip that handles the power and speaker output, and most crucial to the feasibility of adding S/PDIF, a TLV320DAC3203 I2S DAC.
On the top board, there's the array of 7 microphones, 4 TLV320ADC3101 ADCs, and some mystery ASIC marked R3018. It's clearly handling the LEDs and maybe even interfacing the 4 ADCs?