We've finally found the brains of the operation, the logic board!

Apple APL1021 A9X 64-bit Processor

SK Hynix H9HCNNNBTUMLNR-NLH 16 Gb (2 GB) LPDDR4 RAM (2 GB × 2 = 4 GB total)

Toshiba THGBX5G8D4KLDXG 32 GB NAND Flash

InvenSense MP67B 6-axis Gyroscope and Accelerometer Combo

NXP 65V10 NFC Controller (also found in the iPhone 6/6 Plus, as well as Nexus 5X and 6P marked NXP 54802)

NXP Semiconductors LPC11U37 ARM Cortex-M0 Microcontroller

Apple (Cirrus Logic) 338S1213 Audio Codec