I can readily envision that in many homes dedicated lines for the stereo system may be helpful, notwithstanding my comments about power cords not making a difference. For instance, if other devices such as heaters or refrigerators are pulling large currents through lines in the house that are also supplying the stereo system, the system would see less voltage than if fed via dedicated wiring. The miles of wiring outside the house are typically much larger gauge than those within the walls, and are designed to support much larger currents without significant voltage drop. Also, dedicated lines could conceivably help isolate the system from rfi produced by those other devices.
In general, the better the design and quality of the power supply circuits within the system's electronic components, the less sensitive I would expect those components to be to dedicated vs. non-dedicated lines and ac line conditioning.
In general, the better the design and quality of the power supply circuits within the system's electronic components, the less sensitive I would expect those components to be to dedicated vs. non-dedicated lines and ac line conditioning.