Here is detailed information on how to add your Toontrack product as a plug-in in Cubase.
This guide was made using the mac Studio One version 6.0.2.
First open the Effects or the Instrument tab depending on the type of plug-in you want to add.
Find the Instrument plug-in (For example EZdrummer 3, EZkeys 2) or Effect plug-in (EZmix 2, Toontrack Audio Sender) in the Studio One explorer to your right.
When you have found the plug-in you want to add, click and drag it to the track you want to add it to, or to an empty spot on the Studio One timeline.