I actually love this conversation, even if it doesn't solve the original dilemma. I'll admit I don't know which is a closer approximation to the human voice, but Wolfgang's response reminded me of Peter and the Wolf, which, as you may know, creates all of the characters' voices with musical instruments - along with a narrator. I think it's a great teaching and learning piece.

Thanks, Bill D. for that link - it brought back memories of Benny Hill.
Thanks, Alec, for the Electric Sitar reference - I'll try to locate the piece.

As for replicating instruments with the voice, besides someone like Bobby McFerin