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.