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"Back-EMF"

Your explanation is confusing. "Back-EMF" is generated by a conductor moving through a stationary magnetic field. It is called 'back' because it is in a direction that would cause a current that would cause a magnetic field that would oppose the motion. This state of affairs is called Lenz' Law, and is the electrodynamic version of the guarantee that perpetual motion machines are impossible.

Back-EMF in a speaker causes a current that causes a magnetic field that opposes the driver motion. The resistive losses in the amplifier-speaker circuit cause damping. The amplifier appears as a virtual resistor (output impedance, related to damping factor) which is added to the real resistances of the wiring sections. Solving the second-order differential equations reveals that the total circuit resistance determines whether the system is under-, over-, or optimally-damped (the mechanical damping is assumed to be independent of the resistance).

Maggies have low driver mass, but the mass of the air in contact with the panel is part of the load. Since rooms have boundaries, there will be some additional resonances that affect the panel motion, and the amplifier has to damp these as well for optimum bass. IME, the back-EMF with Maggies is so weak that zero amplifier output impedance is as close to optimum as one can get.

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