xtal 18.288Mhz

The closest standard 48 kHz PLL mode on the ADAU1701 is 18.432 MHz (384 × fS) mode.

At 18.288 MHz you would have to run the system at 47.625 kHz.

You'll need to connect the PLL_MODE0 pin to VDD and the PLL_MODE1 pin to GND.

You'll also need to set the sample rate for all cells in the SigmaStudio project to 47625 Hz by following steps 3 and 4 in this post. You need to set and propagate the sample rate for every input or source cell in your project.