mrpippy2...you can use any compressor that accepts side chaining. Sonitus is fine. When I'm in Reaper i also use the inbuilt compressor. They are all good for the task. In fact i only use the compressor, EQ, gate and other basic plugins that comes with my DAW and at least I can be sure that the routing will work.
Ghost track is a copy that is only used as a side chain signal to other tracks and no audio output.
Ghost track because sometimes you what the "pumping" going on even when there is no drum kick playing.
If you want to learn more i suggest you to watch some youtube tutorials. Doesn't have to be DAW specific as these techniques are very similar in every music program...