Is there an 8 channel version of the ADAU1979 ? Need balanced analogue inputs, so the ADAU7118 is not applicable.
No, for 8 channel application you need to use two ADAU1979's. The serial port supports TDM8 operation so two 1979's could be connected for 8 channel operation. The ADAU1979 supports the balanced inputs. See the datasheet.
ADAU7118 is PDM-I2S converter not an ADC. Typically used with digital microphones.