I'm working on a similar project as well, but mine is complete overkill in comparison to what your trying to achieve. Mine is based on a pair of ADAU1442/5 and a pair of ADAU1966.
All Digital Inputs are going to be available on board edge for the DSP's, Spare DSP outputs are going to be routed to the side for an Digital Out board in case you want to experiment with different setups. The DAC's will have all 32 Channels of balanced audio on the other side of the board. Control will be through I2C ( Hifiduino).
USBi will be on the Digital Input board and tied into I2C bus as the DIX9211 will handle all the digital input switching. On the Output board a DIT4192 will be handling the digital output.
Good luck...