Bill, as Rick suggested, you really should use the 8 ohm setting. The statement in the manual is largely because of legal liability problems and the 8 ohm setting in practice is better in the vast majority of cases. The 4 ohm setting reduces the voltage which the amplifier operates at and therefore the maximum current and power which can be supplied. Since one form of Ohm's Law is that current equals voltage divided by resistance(I=V/R), when R is 4 ohms rather than 8 ohms the idea is to reduce the V so that the current doesn't get too high. But since Ohm's Law is also that power(in watts)equals voltage times current(P=VxI), reducing the maximum voltage and current available likewise reduces the maximum power available. Although the need for power is often grossly exaggerated by users, it should only be limited as a last resort(i.e. if the amp would continue to shut itself off). You shouldn't hesitate to try the 8 ohm setting. Incidentally, the fact that the volume settings aren't high in no way means that there's plenty of headroom left.
