Although I've found some info on this subject, I'd still want to ask this question: My receiver is Yamaha RX-V440RDS (rated 6x65W @ 8 Ohm/6x110W @ 4 Ohm, 270W power consumption). The speakers are Yamaha NS-P106 package (Sats/Centre: 30W nominal/100W max, 6 Ohm, Active sub 50W nominal /100W max) The receiver has a speaker impedance setting switch (4 Ohm min. for the main, 6 Ohm min. for the others in one position and 8 Ohm min. for all in the other position). In theory, I know that the correct setting for my setup is 4 Ohm. I also know that changing the position should not alter the sound in normal conditions. The thing is that changing the switch to 8 ohm increases the dynamic range of the sound (it can certainly be felt, the sounds become better defined and the bass is rock hard an still deep) while the 4 Ohm setting produces a silky soft sound, which is not bad, but lacks definition and dynamic (at least that's how it seems). The problem is that I'm not sure what sound I like better. There is slightly higher heat dissipation when the switch is to 8 Ohm. In 4 Ohm the receiver hardly heats at all. Finally the question is: Will leaving the switch to 8 Ohm position harm the receiver in some way on a long term? I would appreciate opinions on this subject. Also on the sound difference thing. Thx.