Dean, I'm not sure what "between all its channels" means. You don't add up the power each individual speaker uses to determine what the amplifier rating should be. For example, if five speakers were using 100 watts each(doesn't happen simultaneously in home use), a 100 watt, not 500 watt amplifier would be needed. The usual 2-channels driven at max for 5 continuous minutes rating, as required by the FTC regulations, is fine for real world application where all the channels aren't simultaneously driven at full power.
My general view is that unless more maximum power than the receivers with ratings in the 100-150 watt area can output is actually needed, the cost effective buy is the receiver. The economies of scale involved with receivers as compared with separate components practically amounts to paying the same or less than what a separate pre-pro with similar features(if available at all)would cost and getting the amplifier for free. If more maximum power was actually needed, a professional amplifier rated for at least 500 watts(less doesn't make that much difference)should be considered as a relatively inexpensive alternative.
