Control Room: How to setup Monitor Sources???

Sorry that this thread now refers to more than one issue, but in answer to your question here are a few threads that refer to the DLL/VST Plugin limitation issue (there are many more):

On Windows operating systems it is only possible to install a maximum of 256 DLL’s or Plugins, however this limit is dramatically reduced by Steinberg DAW’s and in my experience the number installable seems to be reduced with every update.