FenixOZ said:looks complicated, but jsut make sure you stick to the ranges listed on this diagram, it helps things keep sounding authentic.
http://www.dolmetsch.com/musrange.gif
use expressive samples, you need to have a raspy sound on brass rather than a smooth tone.
layer up everything, i use a few of each instrument with varying modulations and velocitys and envelopes.
this applies to all orchestra emulation to be fair, a large amount of effort required.