Hi Adrcula,
Unfortunately I think I discovered another potential problem. You listed the following input/output requirements:
DSP1 to DSP2 - 16Ch
DSP1 to DSP3 - 16Ch
DSP2 to DSP3 - 16Ch
DSP3 to DSP2 - 16Ch
This requires 32 output channels from DSP1. Unfortunately, the ADAU144x family only has a maximum of 24 channels output. Sure, any of the serial ports are capable of up to 16 channel operation on a single data pin, but the grand total of channels in use must be equal to or less than 24. This applies to both the serial input ports and the serial output ports. So, you might have to rethink the architecture a bit.
The ADAU1452 might be a good solution, since it can do up to 48 channels total (input side and output side). However, in that case, you're more limited by the number of pins. There are only 4 data input pins and 4 data output pins. So, you'd have to use TDM8 or TDM16 for the inter-DSP data lines instead of strictly keeping to TDM4.