First off, from the point of view of the linear theory of sound waves, you're plain wrong. Two waves of any frequencies will only interact additively in linear

First off, from the point of view of the linear theory of sound waves, you're plain wrong. Two waves of any frequencies will only interact additively in linear media -- so no low frequencies are created through their interaction (unless non-linear effects come into play, but those usually create higher, not lower, order harmonics afaik). Beating is merely an interpretation of a modulating wave, the reality is the Fourier spectrum. Second, as far as I know our hearing is composed of linear excitation elements (they have a definite bandwidth), and this is confirmed pretty well by experiments with human hearing -- you can see the threshold of our hearing at about 20kHz and that we experience tones of different frequencies fairly independently. Those assumptions imply that two tones, one at e.g. 50kHz and another at 50.001kHz are inaudible, end of story. You can actually do this experiment yourself if you have a signal generator that can do 1Hz amplitude modulation and drive a transducer with a non-negligible sensitivity in that range.