For those interested, I've seen the insides of the M2 and M4. All the specs below are identical in both the M2 and M4. The ADC in the M4 is the same chip but supports 4 preamps instead of 2.
M2 & M4 chips:
ADC - AK5552VN (AK5554VN in M4)
DAC - ES9016S
Integrated Circuit - XMOS U11680C20...