The only video I could find of the studio version of Sofa #1, from the masterpiece album One Size Fits All (1974).
And the crazy wild vocal version, Sofa #2, from the same album:
My off-the-cuff theory about this pair is that in Sofa #1 Zappa initially set out to create a mock heroic composition. But it ended up being so soaring and lyrically beautiful that it stopped being mock heroic and became just plain heroic. So Zappa made the over the top vocal version, to tear the song down, to try to reduce it to comedy. Then he probably wiped his brow and said, “Whew! Close call.”
But the beauty keeps breaking through, even with the crazy vocal version.
The Wikipedia entry for Sofa says that Ya Hozna from the album Them or Us (1984) has Sofa Number 2 played backwards. I checked it out on Youtube. It’s awful. It’s a tedius metal vamp played over a distorted vocal track which must indeed be Sofa Number 2 played backwards. So, I guess Zappa found a way to kill the beauty of Sofa after all.