you do not need any thrid party plugin. Sonar supports MIDI VST. Simply do the followinglfm wrote: What Studio One allows though is routing one midi track to another - making use of VST midi plugins. But this is easily covered using DDMF Metaplugin or BlueCatAudio Patchwork - to load multiple synths and plugins in one go in Sonar X3...
1. Set the plugin as instrument in plugin manager (if not yet the case).
2. Insert as synth and activate MIDI Out.