Actually, there is an excellent reason for using music created with natural acoustic instruments rather than synthesizers or other esoteric electronica. We know (at least musically educated people know) what an oboe, piano, violin, upright bass, or snare drum is suppose to sound like. Nobody really knows what an electric guitar washed through five or six little black boxes is supposed to sound like.
If your concern is only to find a sound that you like, then you can of course use any source you want. If you desire an accurate reproduction system, you'd better start with a known source.
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