Regarding the comments about resistance and voltage drop, as I see it a couple of things should be kept in mind:
1)In the "New Heavyweight Contender" link which Dave provided, the highest resistance shown for any of the receptacles listed is 2.7 milliohms. That is 0.0027 ohms. Even for a large current spike of say 20 amps, that would result in a voltage drop of only 20 x 0.0027 = 0.054 volts (about one-twentieth of a volt). For components other than power amplifiers which draw large amounts of current, the resulting voltage drop would be way less than that.
Given typical gauges and lengths of the house wiring, turning on a 60 watt light bulb that is on the same circuit as the audio system, or leaving a low powered line-level audio component in the system turned on while it is not being used, will result in the AC voltage decreasing by about as much or more than 0.054 volts.
Furthermore, for audio components having regulated power supplies (although that excludes most power amplifiers), that very tiny voltage reduction will be reduced much more by the voltage regulator circuitry in the component.
2)Presumably there is a specific line voltage at which a particular component will sound its best, say 120.0 volts for example. If the AC voltage at the particular location happens to be higher than whatever that number happens to be for a specific component (and it is extremely common these days for AC voltages to be significantly higher than 120 volts), minimizing resistance and consequently voltage drop in the receptacle, the power plug, the power cord, etc., may actually degrade the sound, if it makes any difference at all.
Regards,
-- Al