When Pioneer first introduced the ICE amplifier section, the receiver had a known issue driving 4 ohm speakers.
I agree power is power if everything is equal, but the SC-09 and SC-05 had audible problems when playing hard to drive speakers at a relatively loudness. I know from experience.
"Driving 4-ohm loads was an entirely different story. The SC-07 simply fell apart when running full bandwidth (20Hz to 20kHz) continuous power measurements. As I tested at frequencies above 5kHz with only 1 channel driven, the internal cooling fan would instantly come on right before the receiver would go into gross distortion and shut down at levels above 100 watts. With two-channels driven, I was able to squeeze out a clean 150wpc at less than 0.5% THD. Anything higher would again run the amps into gross distortion and shut off the receiver. I was a bit perplexed in how the receiver managed to better cope with 2 channels driven over 1 and could only surmise that it had something to do with symmetrical load balancing on the power supply. How this receiver was awarded the THX Ultra2 rating was a bit perplexing to me."
Pioneer SC-07 Measurements and Analysis