Pre-outs of many receivers have pretty much standard impedances and output voltages to drive most commercial power amps to their rated power. Am talking about SS gears. Ideally power amps are there to drive and control your speakers as neutrally and transparently as possible. (And the player/pre-amp's sonic character dominates, though even a player and preamp should be neutral and transparent.) But that's more than I can say for some power amps, especially those built for receivers. As far as quality contribution is concerned (sonic coloration), generally, both will have a say. Personally I prefer the more neutral high current NAD amps. Many AV pundits in other forums use a Yamaha receiver as a preamp, even the mighty Z9 paired to a multichanel Aragon or Bryston power amp. Yamaha preamp/processors in recievers are excellent and can almost match in features anything Krell and Sunfire standalone preamps costing twice can offer.
Having said that, I would suggest you try out the config you want. Part of the fun in this hobby is experimenting between gears where you have a number of reasonable options to play around with. For as long as you're not shorting out anything in your connections, or overdriving/under-driving a component, try those options and hear for yourself if any improvement comes out. This hobby is a learning process.
