On the 3RX maybe, but not on the 4RX.
Its an 835 watt system on the 4RX ML system and by switching from a 3RX ML to a 4RX non ML, Im pretty sure the Pioneer 12 speaker setup is probably around that figure too. In fact, I heard very little difference in sound quality in the ML 4RX 450h that I had in the USA last week to my 4RX.
I can remember it was the same with the 3IS too, I deliberately didn't look for ML because the 8 speaker setup is almost as good.