I've done this with MIDI tracks. MIDI is so, so much more editiable.

After separating in MIDI, I often assign horns from different synths to different parts so it sounds like players with different tones, I sometimes "stretch tune" them a bit, stagger the attacks just a tiny bit and do other things to make them sound what I think is better (hopefully the audience agrees).

For pre-recorded tracks, I doubt it's possible.

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Bob "Notes" Norton smile Norton Music
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