If you use the LightWorks Rendering Engine, it will take advantage of multiple processors. Other parts of AC 8/9 will not.
As far as Athlon 64, there should not be any issues, ArchiCAD runs on AMD processors just as well as on Pentiums. I have been using AMD processors for the last circa 7-8 years. They always worked well for me. Also, AMD is cheaper and faster than comparable Pentiums (according to most reviews).
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AMD Ryzen9 5900X CPU, 64 GB RAM 3600 MHz, Nvidia GTX 1060 6GB, 500 GB NVMe SSD
2x28" (2560x1440), Windows 10 PRO ENG, Ac20-Ac27