I have to admit some confusion on this point, since this specifically refers to "combination self-powered speaker systems," which does not apply to anything Outlaw manufactures - they're talking about HTIB systems with separate amps dedicated to distinct and separate parts of the audio spectrum.

In this PDF are some details on this issue, about halfway through the doc. Important is that they distinguish these systems' ratings from standard amp power ratings, because they figure a sub or sat amp in a HTIB system wouldn't necessarily tax the power supply to the detriment of the other amp at peak levels, since unlike stereo amps they each cover different freqs. This refers to the fact that the Amplifier Rule requires testing to be done for both channels of an amp simultaneously, not just one, since one channel will have higher and cleaner output independently (and would be misleading).

To my knowledge, the FTC Amplifier Rule has not been updated specifically for multichanel amps, so "all channels driven" should still mean that all channels are driven with the same test tone simultaneously.