The speakers, according to Paradigm, are"compatible with 8 ohms". Pretty vague, I guess. Mine measure between 3.8 - 5.7.

I have moved the wires around to all the channel outputs, ran combinations of fronts only, rears only rears & sides, etc. While it does takes longer to "thermal" with less speakers connected and in various combinations and locations on the outputs of the 770, it still does.

Measuring the output voltage while running? I don't know that I can tell anything from that - not an engineer by any means. The voltage at the receptacle
stays right around 115-117 vac using a meter, at the levels I have been testing at.

Is a controlled load that a tech would use for bench testing the same as actual speaker loads that vary with music?

Is the resistance variance in my speakers enough to cause a problem? Either way, I have had only the ones with the same measured impedance running at once during this anyway.