Hi Rodrigo --
If you're referring to the Mega Brass voice (8/0/57), the voice itself is a sampled brass section like the DynamicBrass voice (0 127 62) is all of the brass sounds mixed together. So, there isn't a way to separate the voice itself.
However, you could create two tracks, for example: trumpet and trombone. Then, copy the higher Mega Brass notes (middle C and above) to the trumpt track and copy the lower notes (below middle C) to the trombone track.
Hope this helps -- pj