Hello Spalding
The polyphony of the VST is limited by a combination of the VST itself, the CPU and Ram, and not by Wersi. (The large VST sample sets normally have around 256 note polyphony)
Once the VST is loaded in if you wish to use it in the styles you follow this procedure.
1. Select your style
2. Press Quick Edit on the Main Screen
3. Select the voice you wish to change
4. On the screen that appears select the voice you require. (If you require sounds just from the VST, select this in the drop down Window )
5. Save the style in one of the User style banks
6. Map this edited style to a style button. (You can also use the Quickload button on the Main Screen, as each Total Preset (Registration) can store up to 9 different styles)
7. Done. (Whenever you select this style the VST voice will be included)
The Wersi system is designed specifically for ease of use, and in a lot of respects is easier then the PA1X, but not quite as easy as a Yamaha. (If Yamaha do one thing well then ease of operation is it)
All New instruments come with OAS 7 as standard so you will not need to upgrade.
Cost to existing uses (OAS 6) is �370 + Fitting (An Internal Plug- in board has to be changed to run OAS 7)

Lionstracs
You only needed to use the Cubase VST host up to OAS 6, it is not required for OAS 7, however if you upgrade, Cubase is still left loaded into the system, and so can still be used.
Hope this helps

Bill