By orchestra I was referring to all the VST's you are using to create the sound of the orchestra. I assume you are using multiple VST's with perhaps multiple outputs. I was suggesting sending everything into the convolution reverb at a similar level and then returning that to your mix. That is the 'room'.
That convolution reverb though has to be nice and you might have to spend time finding the right sounding room as well. And edit it too for final adjustments.
I agree that percussion can sometimes lack definition as a result of this too but the great thing about this is that I assume you are using different VST's or outputs for the percussion alone so you can send a little less of those parts into the room to improve that. Or perhaps the percussion parts into a second reverb that maybe is a little smaller and less of.
The thing is that you never really hear an orchestra dry. Live it is usually in a rather large space and that adds its own thing to the sound. Even studio recordings of orchestras are in large spaces too and that tends to keep things a bit larger sounding. They can add reverb to studio recordings too and they do.
I also find panning everything as you would see it at a live concert also helps.