One way to add distortion is to run the audio through any of the various guitar/bass effects and amp emulators. Either those that come with Sonar or a commercial or free alternative. Or get an MXR Distortion+ pedal and use it as an external effect. I find that for some reason that pedal seems to work very well on synths and basses, much better than many others like Big Muff variants which are capable of far more distortion when used with guitar. Hardware generated clipping and distortion still has characteristics software can't quite match (yet).
Softube's saturation knob is very good for a digital distortion/saturation tool, as has already been said. And it's free.
Getting much distortion by compression alone isn't easy, unless you're really pushing an analogue compressor or a pretty realistic digital version of an analogue compressor. Good studio-grade compressors don't distort in other than a quite subtle way if at all.