Software synths will often benefit from a touch of saturation, either a console or tape machine style plugin. Some of my personal favourites are the Waves SSL E-Channel stuck across all the mixer channels to give you a desk type feel. The Slate Digital VCC bundle is another one I like and use it in the same manner as the the Waves SSL E-Channel. Another Waves plugin that i’m rating is the Kramer Master Tape simulation, which blows me away when i hear it in action. Tritone Digitals ColorTone is another firm favourite of mine.
As you can see there’s a wealth of options to choose from and I’ve not even touched the service with the ones I’ve mentioned. What I will say is this, “don’t go overboard, just use enough to give you some depth and warmth to make it convincing in the mix”.