Southblend one huge reason to get Sonar is its built plugins like Pro Channel. You are asking about EQ and compression and the Pro Channel excels in both. Sure you need to upgrade to Producer and now X2 but in the end it will most likely save a lot of money for you and you will get some of the best plugins around.
If you notice you don't see a lot of posters asking for compression or EQ here. One reason, Producer has just what you need.
Because you are a Studio user you already know Sonar therefore the transition to X2 Producer wont be a difficult one.
But I must add this too. The Sonitus EQ and compressor are not bad plugins. In fact they compare well to very costly ones. If they are not good enough for you it might not be them but how you are using them.
One thing I have noticed is many people underestimate the quality of the bundled plugins CW provides. Really the only rational reason to go out and buy a plugin is if you need it because you don't have one like it.