Hello Graeme,
OK, then you are running in Master mode. The sample rate will be 48K. It would be best to use the ADC clocks to drive the ADAU1442 so clock domain 1 would be what you use in the Sigma DSP.
Now, in looking more closely at the ADAU1442, you will need to do one of two things in the hardware. Either move the ADC clocks to one of the assignable input/output clock domains. That would be clocks 3-8, just one of them not all of them. An alternative is to move the DAC clocks over to one of the input/output, or just output, domains. Clock 9-11 are output only clock domains.
The problem is that the serial output ports can only be clocked out using domains 3-11 and the input serial ports can only use 0-8. Domains 3-8 can be used for either or both. So you can move the ADC to clock 3 and use it for both the serial input and output ports or continue to use clock 1 for the ADC data and move the DAC clocks over to an output domain. What ever is easiest to do on the PCB.
Let us know which one you did. I will not be able to setup a SigmaStudio project for you until later and I would guess that Brett will not be able to for a little while. To speed things up a bit, make the hardware changes then send me the project you currently have. I can take a quick look at it sooner and offer some suggestions but it will be a while before I could bring an eval board into the lab and supply a tested project.
Thanks,
Dave T