Octane requires NVIDIA Cuda cores to work .. so AMD gear will be no good. Octane X is probably aimed at the newer Macs that can support an external graphics enclosure in which you can put whatever GPU you like in there. There are nVIDIA drivers for Mac OSX still .. but I can't imagine this working on any Mac Prior to 2019. Which is too bad .. I have a 2013 Mac Pro with twin AMD D500 GPUS .. but they're totally useless for Octane.
This is just my opinion and thoughts .. but it's based on what I know about Octane .. perhaps there is a different opinion?
Win 10 Home Edition - Intel i7 5960X - X99 Deluxe II MB - 64GB's GSKILL 3600 RAM - 2x TITAN X (Maxwell) - 1600 Watt Power
DAZ3D - BLENDER - OCTANE STANDALONE and PLUGIN FOR DAZ - OCTANE PRIME for DAZ