Hi Cat,
That's what manufacturers did (and continue to do) to inflate the power output ratings--measure the output at very high distortion levels. I'm surprised that Marantz was honest enough to actually specify 10% distortion ratings; of course that's totally unacceptable for hi-fi purposes. Those sorts of specs were quite common on the power output ratings for after-market car audio in-dash receivers, whose real power output was about 3.2 watts per channel. Car audio builders would advertise the power output as 15 or 20 watts per channel (not quoting the distortion at those levels which would be at least 10% or more) to inflate the power output ratings.
Even now, some manufacturers of AV receivers (Onkyo and Yamaha, to mention two) continue to quote the bogus "dynamic power output" specs, which will yield huge power output levels because they don't state the distortion. The latter may be as high as 20% or more.
Regards,
Alan
