The figure below depicts an amp running trans-tenuated, to half power, into a pair of speakers. In this case only one speaker is being driven, by half of the amplifier's full power, identical to the way it is driven in the unattenuated, full power case. As a result, cone breakup level is identical when the amp is running trans-tenuated at half power and unattenuated at full power!
The figure shows only two speakers, with the amp running at full power. But the key conclusion - that the lone driven speaker is driven exactly as it is driven in the unattenuated, full power case - also holds for the the amp running at less than full power. It also holds for the much more general cases of pairs of identically rated speakers networks or more general amplifier loads.
