I'm currently pretty excited about the Chris Lord Alge extension for SSD 4. The groove is critical to a great sounding mix and for that you have to get those low end rhythm sound sources like kick, snare, bass, percussion, toms cut through much enough, yet soft enough. These days I prioritize the drum and percussion (rhythm) element as nr 1, with that you get a powerful foundation. It ultimately allows you to get a smoother transient balance and with that comes gained mix signal and size. Side-chaining is almost like a way of prioritizing sounds in the mix, it's almost better than the volume faders. I also think that various side-chaining techniques are worth a lot when it comes to making drums sit in the mix. The drums need to be soft enough in order to make the listener attached to the mix. One technique I've used lately for kick and snare in general has been to beat the crap out of them until it clips, fine tuning the frequencies towards softness, definition and punch in that hard grip and then loosen the compressors' grip on them until they are big, warm and emotional in the mix. It's all about taking those small sounding raw samples and making them sound big and real, and that's challenging.
I think the trick is to mix every kit piece separately on dedicated FX chains, in solo until they really sound stunning all by themselves, as if each kit piece were the main instrument in the track. EZdrummer has in my experience been very challenging to make great sounding.