Charles, again the reason for strongly suggesting that manual directions to set a lower impedance number be disregarded is that this in no way "optimizes" the receiver for lower impedance speakers, as some imagine. It's a safety precaution to keep the UL happy by reducing the chance for overheating at high volume levels and it does this by reducing the maximum voltage that the power supply can output by something on the order of 25-30%. Since power is proportional to voltage squared(Ohm's Law again)this sort of reduction roughly cuts the maximum power capacity in half, as test labs such as S&V have reported. For example, if the maximum voltage output was 40 volts otherwise, setting the lower impedance switch or menu setting might reduce this to about 30 volts or a bit less and power capability would be roughly halved.
Whatever better results you may get from your experiments, there doesn't appear to be a reason that setting the impedance lower would be a positive factor.
