There is a difference, how significant it would be is up to your ears/wallet to determine.
Why the curiousity about these particular amps? You do know that the Proceed line no longer exists don't you? Do you also know that Madrigal no longer owns/markets Proceed/Mark Levinson components? Harmon International owns them now. FWIW, I have heard that service can be an issue, are you aware of this?
I would think that unless someone was giving them away, I might be looking for another amp. There are many good ones out there, even on the used market.