In Jive 6.0 the content search sub system was significantly refactored as we rolled out our Cloud Search platform. It is not possible make any customizations to content search if you are using cloud search and so if customizations are necessary then you will have to use on-premise search. However, given this new service architecture the task of adding new fields is considerably more involved since it requires modifying the Ingress activity objects in the core web app code and the corresponding classes in the on premise search component. In short, it's far too complex to outline here.
I would advise seeking assistance from our professional services group.