Zap, when it comes to amplifiers, including those in receivers, the term "high end" is pretty meaningless unless it's used to refer to price rather than sound quality. All competently designed amplifiers, certainly including the Pioneer, Denon and Onkyo models you mention, amplify transparently within their designed power limits and don't add any audible coloration to the sound. Neither the Onkyo nor the others had sound quality in the "low to mid range" and there's been no change in that. Choose based on features and price.
