Consider the following statements:

"For a fixed amount of an ideal gas kept at a fixed temperature, pressure and
volume are inversely proportional."

Right? Now this one...

"Boyle's law is used to predict the result of introducing a change, in volume
and pressure only, to the initial state of a fixed quantity of gas. The before
and after volumes and pressures of the fixed amount of gas, where the before
and after temperatures are the same (heating or cooling will be required to
meet this condition), are related by the equation P1V1 = P2V2."

See the disclaimer? Compressing/expanding a non-ideal gas heats/cools it.
Assuming that both air and SF6 are non-ideal, this produces a non-linear
restoring force. SF6 is supposedly closer to ideal, so it should provide lower
distortion in a "true" acoustic-suspension system, where the gas provides a
big percentage of the restoring force.

You'd better give up, because I'm going to keep posting this until you do.