Thanks for providing the link. Zero autoformers are normally used to increase the impedance seen by the amplifier, so I had assumed that your reference to using resistors as an alternative referred to inserting a resistor in series with the speaker, which would raise the impedance presented to the amp. But I see in the Zu writeups that what they are referring to is placing a resistor in parallel with the speaker, to **reduce** the high impedance some of their speakers would present to the amp.
A Zero autoformer can be connected "backwards" to accomplish the same reduction in the impedance seen by the amp, but the need to do that would only arise in uncommon situations. And in those situations I would expect that the large cost difference between the two approaches would make resistors the preferable alternative.