stevec
- Per instrument tracks (no chords)
- Don't be afraid to duplicate each individual part using multiple samples/synths
- Pay attention to velocity and note overlap to get the most natural sounding "feel" per part
- Leave just a little "slop" in start and end times so that the combination of parts seems human
- Pan and blend until it sounds right to you
- Use a nice small room/plate reverb to emulate a cohesive section
That's all I've got. 
Which all works great for individual instruments, and the way to go, if you had a wind instrument controller, that would be better
he asked about using session horns
but session horns is an "automatic" section, that populates a set with certain horns(trumpet, sax, trumpet, etc)
and does divisi based on note/chord input. lots of flexibility in drops, legato, etc in the program and the riff generators, but you have to approach it as a horn player and not as a keyboard player voicing organ, piano etc
I have had some success with session horns and SH pro, but it takes some forethought