Can I use an ADAU1761 as a drop in replacement for an ADAU1961 with no register or setup changes

I have a currently working board fitted with an ADAU1961 CODEC. This has registers manually configured from an attached FPGA device. Having looked at the pinouts and register descriptions of this device and an ADAU1761 CODEC (which includes a DSP) it would appear that I should simply be able to fit the 1761 in place of the 1961 and it should function exactly the same. It doesn't. No audio comes from the device. The attempt here is to be able to do some DSP processing in future but at present I'm just trying to prove that the 1761 will drop in, in place of the 1961. There isn't a Sigma Studio project for the existing 1961 part and looking at the register set for both devices it would appear that the default settings for the additional registers associated with the DSP in the 1761 should be fine. Nevertheless no audio! So what, if any of the new registers need to be set to simply "bypass" the DSP and make the 1761 just behave as a 1961?