Tim--
To over-simplify, getting an organic sound is largely a function of "change."
Change the dynamics and timbre of your phrases with modwheel cross-fading instruments.
Change the expression and volume of individual notes (esp. long notes) with midi CC#11.
Change articulations.
Change tempos. Add subtle ritards and acccerandos.
If you quantize, go back and randomize the start and end times of notes so that instruments do not start and stop at exactly the same time. This will prevent that "organ" sound esp. with woodwinds and brass.
Create “width” by panning and placement of your instruments. Create “depth” with your reverb. (There's a good discussion of this in the mixing forum.)
There’re many other tips, but I either don’t know them yet or am too tired to think of them right now. Maybe we should create a separate thread and everyone can contribute their methods. I think this could be very helpful to many (myself included)!
Mike--
What you describe should work nicely if you have the cpu and hard drive speed.
My computer is too slow, so I had to record premixed dry tracks of each section (4 in total) in Sonar. I created a wav file of each premixed track, loaded the wav file into GS3, and then routed this one wav file through a single instance of Gigapulse. I then recorded the resulting wet version of the premixed track back into Sonar. When I had done this for all 4 premixed tracks (using different settings in Gigapulse for each section), I mixed the 4 tracks together in Sonar. Admittedly, this is not the simplest of methods, but it works.
Best,
Jay