My Pioneer 45TX can also drive the 4-ohm fronts (Hales System Two) plus the 6-ohm VP150/QS8's at the reference level and beyond, even though Pioneer (like Onkyo) recommends >6-ohm speakers. Although I do not remember the actual impedance curve of the Hales published somewhere a long time ago, I don't think it was as well tamed as the M80, which is shown below...