Hello,
I have successfully connected Studio One 4.6.1 to Vienna Ensemble Pro and created a couple of instrument tracks that successfully plays the loaded vienna instruments pro instrument (in this example chamber violins and chamber violas). I can hear the various pitches when I use the keyboard in Studio One but the keyboard on Vienna Instruments Pro (which is hosted in Vienna Ensemble Pro 7.0.954) is disabled. In other words clicking on the keys on the Vienna Instruments keyboard do not work and there is no sound. When clicking on the keys in the Studio One editor the keys on Vienna Instruments Keyboard do press down but I can't get it to work directly from Vienna Instruments Pro. This is important to me because I sample heaps of different articulations in Vienna Instruments and I don't want to go back and forth from S1 to VEP to click on keys. I am not using a midi keyboard. I was able to do this fine in Logic Pro X