I will take full power frequency response for $100 Alex. I will pass on the "complicated ham sandwich" bonus.
Real audio, not test signals, is bandwidth limited. Square waves, slew rate, etc. complicated ham sandwich measurements. Mathematically its a bunch of sine waves, and they don't have infinite bandwidth, 20KHz, pretty much. Even if the source supports > 20Khz, you will find there is never full power harmonics at those frequencies.