Regardless, if the output levels are closely matched, one amp /will
not/ pump current into the other. But to gain any increase in power,
you'd have to use a lower-impedance speaker.

You are VERY WRONG on this.

Why? You haven't changed the output voltage. If the amps are solid state,
their source impedance is much lower than that of the load, so there
wouldn't be any significant increase in current flow (that I know).