Hey Steve, thanks for the reply.
They were actually given to me in return for a few days work last year.. And yes they are the 70's vintage AR9's that weigh around 65kg's a piece. They've just been sitting idly by some Infinity SM-155's that I've been running with the Yamaha setup.
I do like the Yamaha gear but was willing to part with it if need be. In regards to powering the AR's, I really wanted to find something of similar vintage. I agree though, something like the M6500I would definitely make them sing.
I've also heard the AR9's run quite nicely when bi-amped. Just a matter of finding two vintage powerhouses up to the task I guess!