Hello Lionstracs
The number of VSTs that could be loaded into the Cubase version supplied by Wersi, was 4.
Owners who required more usually purchased Steinbergs VSTACK which allowed up to 16 VSTs to be used.
The main problem with using VSTs is that (Depending on the type) they use up CPU power and Ram, and if you use too many at the same time you get note dropout or system stutters. (Those that are familiar with VSTs will understand this and will set up a balanced system accordingly)
With OAS 7 the host was integrated but the number of plug-ins remained the same, this was done deliberately by Wersi, as the players buying a Wersi would most likely be coming from hardware based arrangers/organs and so would most likely not be familiar with the above concept, therefore by limiting the number of VSTs that could be used simultaneously, it reduced the chance of players running into problems. (When Dual core CPUs drop in price and are fitted as standard, Wersi will increase the number of slots to suit)
You can load a large number of VSTs into a Wersi and then just select the ones you require for your performance. (I believe with OAS 7 they can also be stored in presets, so that you do not have to set them up individually)
A lot of OAS 7 details you will find in the links I sent you, and also by reading Ensnareyou’s postings. (I believe he actually uses OAS 7, whereas I am still running on OAS 6)
To sum up
The Wersi OAS system is designed to make it as easy as possible for the uses of hardware based boards to make the transition to a software based board.
Hope this helps and if you require any more specific information, just post again and I will try to help. (It would also probably be better to start another thread, as we are starting to get a bit OT)

Bill