The Vienna Organ Player software will be installed in your Programs/Applications folder, and the plug-ins for VST/AU/AAX will be installed in the corresponding plug-in folders (macOS: /Library/Audio/Plug-ins and PT). Use the Vienna Assistant not only to install the Vienna Organ Player, but also the sample content of the library or libraries you purchased. The Vienna Assistant will ask you for a download location and an installation location. You can manage these and other parameters in the Assistant’s Preferences. Make sure to select a target location for the installation with sufficient disk space. You will be warned if the hard disk you specified for the sample content does not provide enough free space, or if its specifications do not meet the requirements of the player. In that case, please cancel the procedure and retry, specifying another hard-drive
The plug-in is treated like other VST or AAX instruments. In Vienna Ensemble, e.g., select "Insert Plugin" and choose the Vienna Organ Player:
When you run your Vienna Organ Player for the first time, you will be asked about your keyboard setup:
If your setup includes several MIDI sources which you want to use with the Vienna Organ Player, clicking that button will open the Settings –> Engine section.