TRUE!! I followed up with calls to Denon and Yamaha customer service. Both stated that if you choose 4 ohm in the impedance section, the unit engages a protection feature that will limit the current draw. So while the manuals for both state that you can use 4 ohm speakers, the switch setting is a dead giveaway that the unit handles 4 ohm speakers by limiting the current. Yamaha does this explicitly by recommending 4 ohm speakers be set to 6. Denon does it by setting the option to 4 but in the end, all you are doing is engaging a protection circuit.
Yamaha went further and stated that with 4 ohm speakers, it was fine to leave the impedance setting at 8 and as long as you don't turn the wick up to where your ears are bleeding, the unit will not be harmed. As in a previous post, heat is your guide. The AVR won't blow up if you put a 4 ohm speaker in the same room.
My question, then, is whether clipping is occurring at some point with this sort of system. If so, then the real answer is: if you have 4 ohm speakers and want to attach to an AVR, plan on using an external amp for the LCR channels.
Realistically, I don't think the people buying 4 ohm speakers are relying on their AVR to pass sound. So this is all probably a moot point.
