Soundtoys 5 installs all plugin formats to the following locations. It has no customize option.
AAX: /Library/Application Support/Avid/Audio/Plug-Ins/Soundtoys/
AU: /Library/Audio/Plug-Ins/Components/
VST: /Library/Audio/Plug-Ins/VST/Soundtoys/
Manually delete the AAX and VST versions using Finder after the install if you only need AU.