Nut, first you're mixing the FTC regulations up with UL(Underwriters Laboratories)testing for fire safety. The FTC regs are purely a "truth in advertising" movement to combat inflated power claims which were rampant in the 1970s. What's rather ironic is that this is the only area in audio which is governed by relatively specific and mandatory regulations which we can rely upon, yet some audiophiles who're willing to take seriously unsupported claims about the "sound" of amplifiers, players or even pieces of connecting wire view with suspicion amplifier power ratings.
The text of the regs can be found
here . There's no specific number of channels which have to driven simultaneously given in the text, but the FTC interpretation in practice is to require that it be at least two(one isn't acceptable)and most manufacturers follow that for their basic rating, so two is to be presumed unless stated otherwise. They're free to base their rating on an "all channels driven" and the few that do, make it clear that they've done so. In real world home use the all channels driven number is unrealistic and all channels are never driven at full power for five continuous minutes. Audioholics, for example, makes this clear and tests with one and two channels driven as being more in accord with actual requirements outside a testing lab.
Tests of receivers by Sound&Vision, Home Theater Magazine, etc. almost without exception show that they meet the official(usually two channel)rating.
