To simplify your search (because I know you've probably gone to a zillion pages trying to find good samples of things), here are a few links to some demo mp3 files:
Sample Tank:
http://ikmultimedia.com/sampletank/audiodemo/ There are also a few videos showing how the plugin works there as well - on the left sidebar
the "sounds" one has Dave Kerzner going over a number of the different tones.
Sonik Synth 2:
http://ikmultimedia.com/soniksynth/audiodemo/ There are a bunch of great demos in this list
One cool thing is that you can use SampleTank (which has a deeper interface and more multitibrall parts per instance at 16 instead of 8) and load the SonikSynth samples in, or many of the other packs, like the Miroslav Orchestra library, moog library, etc. You can also easily layer sounds within or between ibraries by simply setting multiple parts up on the same midi channel within that instance - instant layer from a single midi track. You can layer all 16 parts to a single channel if you want, including doing things like a certain amount of morphing between sounds by adjusting each part's envelope settings.
Can you tell I like their stuff?
Downsides: Mousewheel does not work within Sonar to scroll through patches, which is a bit of a nuisance, but the little scrollbars work fine. There's an "alternate version" out there which does make the scroll wheel work and adds some other navigation features as well.
Also, it doesn't seem to pay any attention to ACT, so controllers need to be done with midi learns. I don't know what it is about this synth that it doesn't respond to ACT, but I can't get it to, anyway.
Hope this stuff helps.