Hi Tobias,
the AddOns are divided into RackExtra and Deep.
Deep: 5 Comp Models, 4 GEQs and the Tubestage Preamp Emulation
RackExtra: MultiBD, DynEQ, De-Esser, Echo, HypaBass and Bucket Brigade
Deep AddOns work in the channel processing and RackExtra, as the name suggests, in one of the normal 8 FX Slots. That means you can have a maximum number of 8 MultiBD or DynEQ.
Hope, that helps a bit.
André