I've seen similar experiments regarding amplifiers. I'm willing to reconsider, though I do have questions.
1. I agree there is no magic to be found in amplification as long as the amps under consideration have a flat response. However, amps will not necessarily deliver power cleanly at their limit, which can cause distortion. (I assume this would be mostly due to the quality of the components used.) How would one determine that two amps with 100W/channel ratings would perform comparably at any given output?
2. Don't receiver manufactures often compromise the various components used due to chassis restrictions and price point? Would most modestly priced receivers with a 100W/channel amp cary the same quality of amp components as a modestly priced 100W/channel amp separate? Related to question 1: how would one determine the comparable performance, especially at power limits?
3. How can it be determined that the audio processing of the pre/pro or receiver is flat when compared to the original source before amplification?
4. Isn't there a chance of noise being introduced in a receiver due to the close proximity of the amp and processor?