Now, outlet 5 remains a contractor POS outlet. Its technically past the system, but being that this AC, and not DC, wouldn’t it technically also be part of the AC chain feeding the stereo?No, it wouldn’t. Assuming that nothing is plugged into outlet 5 no current will be present in the wires between outlets 4 and 5. I suppose it’s a remote possibility that the wiring between outlets 4 and 5, or outlet 5 itself, could pick up RFI (radio frequency interference) that might find its way into the system via outlet 4, conceivably with audible consequences. But that seems highly doubtful, and even if it were occurring it would seem probable that it is mainly the wiring that is picking up the RFI, meaning that upgrading outlet 5 probably wouldn’t help.
It could also be argued that the capacitance of the wiring between outlets 4 and 5, and the capacitance of outlet 5 itself, would have a slight loading effect (and therefore a slight filtering effect) on RF noise that may be present on the incoming AC, that is drawn by the system via outlet 4. That too seems very unlikely, but the point is that even if the presence of outlet 5 and the wiring to it from outlet 4 makes a difference, it’s possible that the difference could be for the better rather than for the worse.
Regards,
-- Al