I might need to add an I/O expander to the Pi, I see on the page https://www.hifiberry.com/docs/hardware/gpio-usage-of-hifiberry-boards/
That the I2C is used by the Amp2. Looking at the TAS5756M datasheet I see that the address for the TAS can be one of four addresses depending on the strapping of ADDR0 and ADDR1. I would assume that ADDR0 and ADDR1 are strapped as 0, so the I2C address would be 0x98/0x99. Is this assumption correct?