I looked inside my DR680 and it has an Analog Devices BF523 BlackFin DSP chip. My guess is that after A to D conversion (AKM AK4612EQ), the Blackfin handles all audio manipulations such as routing, mixing, processing, level control, limiter, filters, etc. You have to handle it somehow, AFAIK there is no handling of audio in the analog domain. The AKM handles D to A, too.
Maybe they got a discount on Blackfin chips by writing it on the box!