I'm looking to add a good 5 channel amp to my system, it will drive only the center and surrounds.

First off, I want something around $500. Since the amp is not a requirement, I can't justify a $1500 Anthem or Aragon (although I'd love to!)..so it's the used market for me, but there are SO many!

I'd like to have one with signal sensing auto turn on also. I just need a good list of amps to start. I see B&K, Adcom, Parasound, Acurus, and others that meet the power and price requirements, but none seem to have the auto turn on. Is this not a common feature in standalone amps?