By coincidence, last night I stopped to visit with a couple seated at a table near me. The man asked how I achieved the background singers. I explained to him that it was a device that followed my chords, sampled my voice and reproduced it in the harmonies I pre-selected.
He looked at his wife and said, "See I TOLD you I heard multiple voices, they are recorded ahead of time, like he said."
You can't win, but at least they liked it.