I don't think the R800c is intentionally voiced differently than the R500c. Quite the opposite, I believe the 800s, including the HD head & Stage, were designed to be electronically as much like the original Rumbles 40, 100 200 & 500 as possible. It has been often commented how well the original line "plays well" together, and I'm sure Fender wanted the newer 800s to share in that. But the higher voltage components for 2.67 ohm and 2.0 ohm operation, and of course the Neodymium speakers of the R800c, may have contributed to any perceived voicing difference.