4x8 DSP using two ADAU1701

The Dayton DSP-408 has two ADAU1701's to make it a true 4x8 DSP.  How would I be able to do this on my own?  I have the Sure APM2 that has a ADAU1701.  Is it somehow possible to transport audio between two APM2's to increase the in/out count? Thanks!