At one time, you could find Proteus-X on the net for free. I grabbed it but just spent a few minutes searching with google and did not find it....
However..... inside of MC6 you have a ton of really good synths and sampled sounds. I would not sweat too much over the Proteus thing.
I suspect that at some point you may end up buying DimLE so at that time the proteus stuff will work.
Just checked the CW store..... DimLE is $50 and comes with Garritan (GPO) which has some decent orchestral stuff. There's your ticket to ride.