Actually Sushi, if you look at the dynamic power listings for the Denon 4802 (a model i was considering before i got the Onkyo) and the Yamaha RX-V1, they are 'rated' for 4 ohm loads (2 channel) and both models list ratings down to 2 ohms.
I nabbed this from the manual specs:
Denon 4802 170W-8 ohm, 270W- 4 ohm, 350W- 2 ohm
Yamaha RX-V1, 150W, 180W, 240W, 340W at 8, 6, 4, 2 ohms
I could not find this same info for the H/K, Marantz or Pioneer (although to be fair i couldn't find a user manual for Pioneer).
I may not consider running a 4 ohm speaker all the time with these models but it certainly would depend on how the 4 ohm rating was assessed. If the speaker has several spikes down to 4 ohms but really averages about 5 or 6, then i probably would not be so concerned. If the speaker was more an average of 4 ohm with spikes below that, i would probably look alot closer at getting separate components.
I'm sure that several of these amps/receivers should drive 4 ohm speakers just fine (my Onkyo did) but i agree that the Pioneer protection circuitry might be a bit on the overly conservative side. Perhaps it is because their amps get hot enough just powering 8 ohm speakers that they NEED the protection circuitry more so than some other cooler running brand names.
