Solar Fire contains a built-in copy of the ACS Atlas. It also has the capability of linking to a standalone ACS PC Atlas (but this option will be grayed out if you don't have one installed on your computer).
To specify the Atlas to use click on the ACS (Built-in) or ACS (Standalone) in the "Preferences" dialog, "Places" tab...
After you set this option, whenever the atlas is accessed either directly (by clicking on a Place… button) or indirectly (by using the Autolookup feature), the chosen atlas is accessed.