There are two ways you can integrate PEQ into your system.
1) Use a PC, install REW and a PEQ software and then get a UMIK-1 (USB Microphone) for measuring the speakers and calibrating the PEQ to your speakers requirements for flat response.
2) Use a miniDSP as a PEQ inline between the DAC and the Amplifier. This will require using a single ended connection for connecting the DAC to the mini DSP and then also for connecting the miniDSP to the amplifier. Because you will be using your Apple TV in this configuration as the source the UMIK-1 will not be required unless there is something I don't know but I'm pretty sure it can't be used here.
For #2 alternatively you can use the mini DSP as the DAC and PEQ because it has that capability too.
Stating the obvious here but in this case I would want to keep my DSP in the digital domain and would not want any DSP downstream of the DAC. miniDSP nanoDIGI or OpenDRC-DI would be good all digital options. As a more DIY option a RPi4 + CamillaDSP with a hifiberry digi+ I/O HAT would work well.
Michael