Hi Robert,
It looks like this is an old question, but I'll give it a shot.
The ADAU1772 requires a single address byte, and unfortunately that's not configurable. That is true whether you use the I2C interface or the SPI interface. So, switching between I2C and SPI will unfortunately not solve the issue. The only way to deal with this is on the Blackfin side. I would suggest trying to contact some BF support engineers to see if they can help you implement single-byte addressing instead of double-byte addressing.
I have never used a Blackfin, so unfortunately, I can't provide much assistance with that!