"Another aspect: are the ohm ratings the same for all 3 of these devices? Would they all work via a 401 line card?"

You don't really need to know what "the ohms rating" is, because all three devices are entirely different, have entirely different circuitry and are used in entirely different applications.

You should use the one that the experts and the BSP recommends, because that's the one that is designed to do what you want to do. It is the Spokesman, which is exactly designed for your application.

A plain speaker will not work. A 694 will not work because it requires a special control unit.

Arthur P. Bloom
"30 years of faithful service...15 years on hold"