I'm reading Mike Seniors book about look-ahead plugs that works on the sharp rise in sound rather than a fixed threshold.
This would be great for live input tracks where the levels vary but you want the initial transient to expand.

http://www.stillwellaudio.com/plugins/stillwell-audio-plugins/transient-monster/
One relatively affordable example

M_Glenn_M
http://www.stillwellaudio.com/plugins/stillwell-audio-plugins/transient-monster/
One relatively affordable example

Don't know if you have Komplete, but Transient Master in that package looks like the equivalent of the Stillwell one. It's also great on guitars and keyboards as well as buses. 

No Komplete but thanks for the name.
Yes I can see a lot of use for this kind of plug.
Worth paying for even :)

You could play around with the TS-64 Transient Shaper

Is this not triggered by a volume threshold?

Hi M_Glenn_M
Hmmm, I think there may be some confusion here. A transient shaper will work on a sharp rise in sound in every case. That's what makes it a transient shaper. A threshold independent transient shaper should affect all transients, while a transient shaper with a threshold will work only on transients that exceed a specific amplitude. Theoretically that threshold should go low enough to include ALL transients, thus making it effectively "threshold independent".
So, a Transient Shaper with a threshold should work exactly the same way that a transient shaper without a threshold works, just with another level of control. Or specifically, the TS-64 should work the same way as N.I.'s Transient Master, only you can specify the places it does not take effect with the threshold. I own the Transient Master (and of course the TS-64) and haven't A/B'd them, but the TS-64 should do the same thing as the Transient Master only with better control granularity.
 
Of course, variation probably exists as with any other plugins from different manufacturers.
 
Hmmmm....maybe I'll A/B a bit later, but they should do essentially the same thing.
 
Dean

OK, just A/B'd and they (to my ears at least) do the same thing. Actually, I had forgotten the TS-64 existed until I read this and now that I put it next to N.I.'s Transient Master I think I like the TS-64 better. It's MUCH more controllable and (again to my ears) sounds just as good...probably better given the tuning options available let me change the sound of the transients to match what I want. 
 
Shorter answer - the TS super cool for getting more "click" on kick drums, particularly since i can "tune" the transient higher to pitch the click where I want it.
 
Dean
 
EDIT: In fact, now that I think on it a bit more, it seems to me that all transient shapers must have a threshold. Otherwise how could they determine what is and is not a transient? If that is the case (as seems likely), it's probably more accurate to refer to fixed threshold transient shapers and variable threshold, as opposed to threshold dependent and independent. 

I was confused about the threshold on the TS 64. 
This is perfect and a great Sonar inclusion. Glad I asked.

Danny did a video on how to use the Transient Shaper a while back...
 
http://forum.cakewalk.com/tm.aspx?m=2795310