Bernd,
I'll assume you're very new to Studio One, just to be detailed in my instructions. Hopefully this helps.
In Studio One, add an instance of the Vienna Instruments plugin. Then right-click on the Mixer and click "Add FX Channel". There is an arrow in the middle of each channel strip to expand each channel. In the expanded view, you can use the "send" option to send the audio signal from VSL's plugin to the FX channel. I believe the only difference between FX and Bus is that FX stops the signal chain. Buses can be sent on to other buses (something I typically avoid myself). Honestly, the only way to get a feel for what will work for you is to try it. Like everything in life, it takes practice (aka: trial and error). So I hope these instructions are helpful, but you may have to get your hands pretty dirty to figure out what you like in the end.
Unfortunately music software has a much more confusing learning curve than the real world of the orchestra (IMHO). I'm working on taming that though. 😉
-Sean