The 650A had a fine write-up this year, but was superseded not long afterwards by the latest in the Marantz line - the PM6003. I've heard the 650A, but, as with most Richer Sounds branches, this was in the middle of the shop rather than at home, so it's rather difficult to say. It didn't appear to be particularly bright or rather, excessively so and Alan Sircom (long standing hifi journo) raved about it last year. He currently edits a very high end title, so the amp was up against some impressive marques.
Pop along, have them play it for you and see what you think (assuming you're in the UK). Might be worth havign a think about the kind of sound you like - if it leans towards more balance/neutrality, then the CA mightn't be such a good fit for you and a glance over at the Yamaha AS-700 (or the recent -500 junior model) might be worth you checking out. See also Harman Kardon, Onkyo, Teac, NAD, Denon...plenty to choose from and fit and finish in most cases can be impressive.
The sub-£500 bracket is stuffed full of some decent amps, so there ought to be something out there that fits the bill. If not, maybe have a think about going down the ex-dem/secondhand route; some dealers offer warranty cover, anywhere from 3 months up to five years in a couple of cases (though maybe not in your budget, but feel free to prove me wrong on this!) and it can be a good way of getting more for your money.