Trying to break this down as simple as possible:

The MC200 is a box
It has a computer in it
The computer has a custom Meridian audio board attached inside the box via USB

The audio board is inside the MC200
The audio board has USB input.

The audio board inside the MC200 is 'like' the Explorer, hence the same lack of FIFO on the data sheets.

There is a picture of the insides on Duncan's site if that makes it easier.