Every receiver I've seen that has a separate 4 ohm setting usually does put a resister in series in the output.This reduces power,but also helps protect it from the low resistance load.In other words,it helps keep the amp in the receiver from overheating,and getting damaged.One way to tell if this is the case,check the power rating for all the channels driven times 8 ohms,and 4 ohms with all the channels driven at once.If it doesn't double,or have a large at large increase at 4 ohms,it probably has a resistor in the circuit. Checking the Integra site,it obviously uses a resistor because its consumes a maximum of 972 watts total including thermal losses. This seems to be common with a lot of receivers.Integra link.[http://www.integrahometheater.com/model.cfm?m=DTR-50.1&class=Receiver&p=s]