I also like the Onkyo A-9555 a whole lot. It doesn't have a sub out, but I've found that some of the <$500 subs sound better with the speaker connections anyway. It also doesn't have pre-outs, and it doesn't have video switching.
What it does have, however, is an insanely low noise floor at its price (essential for HT to hear dialog), great dynamics, great slam and current delivery, and sounds much more powerful and expensive than its price would suggest.
The Onkyo A-9555 now lists at $799 and is worth every penny, but a new batch of Onkyo factory refurbished units are available with exchange privileges and warranty for $429 in black or silver at www.accessories4less.com
It also has a remote you can use by feel in the dark.
I've heard the Cambridge 640A extensively and owned the Outlaw RR2150 for awhile. I've also had various classic vintage amps and pre-amps from Amber and VSP Labs from the '80s that would fit your budget. But I'll take this Onkyo over any of them--new Cambridge or Outlaw or vintage Amber--in a heartbeat. The Onkyo has the Cambridge's detail plus much better frequency extension and slam, and it's faster, clearer, and quieter than the Outlaw.