The real question is that is why aren't audio equipment manufacturers providing cords of adequate guage and proper EMI filtering at the mains input of their expensive amplifiers. Come now, how much cost savings is there between a 16 guage and 12 guage cord? I'd be surprised if it exceeded one dollar of cost to a manufacturer. So why, after spending several kilobucks on an amp or preamp, should I shell out more to make the device function at a level I expected right out of the box? And why aren't audio equipment manufacturers taking appropriate steps to shield and filter their components to avoid internally generate RFI from being radiated or conducted from outside the confines of the box? The engineering principles are long standing and well understood. Why do we insist on elegant industrial design (look and feel) but permit sloppy engineering of the contents? (I think this is one of the distinctions between "consumer" and "pro" gear... and although we may pay audiophile prices, it seems in some cases and respects we're still getting consumer mass-fi grade engineering). If the audio magazines want to go measure something, go do what the manufacturers should be doing: measure the EMI/RFI output and susceptibility. There are well known standards and procedures for doing this.
The fallacy of ac treatment
I see a lot of threads related to managing and tweaking the ac powerout end of electronic systems. Much has been said about dedicated wiring, termination and even the right kind of extension cords to use. I work for an electric utility; and that's the extent of my credibilty here. The majority of you will no doubt be far more erudite wrt music hardware. Just a thought, though: domestic ac distribution goes thus: power station-step up-city-step down-subdivision-final step down. As far as the utility is concerned, you and all your neigbours are collectively the load for the step down tranformer. Any inductance/capacitance created by your neigbour running motors/tubelights, etc is felt by the lot of you. Additionally, the voltage frequency will almost always move around a tolerance from 50hz as the whole country turns on the air, off the lights - changes all the time as peaker plants ramp up etc. Nothing can change that- the frequency of the grid supplying your city is the frequency in the mains at your house. So what's my point? Well only that how much difference can the last 10 feet of cabling, etc make when the other hundreds of miles are outside of your control? And more importantly, frequency is one of the most imp parameters for measuring electricity quality (your expensive hand-coiled toroids are entirely subject to the f in the primaries) and nothing other than running an f generator can shield you from that. Methinks all the improvements you see from ac cord treatments are pyschosomatic. But that's cool.