f4ier, I think you missed the exact statement that Fossil made. He said for an input of 1A (ac). Therefore the reactive part, which is in series with the voice coil resistance, does not influnce the amount of heat generated in the voice coil. This is I^2*R, and so is 8W. Of course, there are other sources of dissipation, such as in the mechanical losses of the supension and cabinet, and in the air load resistance, but these are tiny compared to the voice coil.
Andrew