** The 70V transformer primary probably has a DC resistance
of about 0.5 ohms
At some low frequency, the iron core will saturate, leaving you
with a 0.5 ohm load on the amp - same goes for the transformers
in the distributed speaker system.

That assumes the "some low frequency" gets through to the transformer.

I remember J Gordon Holt's review -- almost 50 years ago -- of the KLH Nine
electrostatic speaker. He pointed out much the same thing, suggesting that a
Really Big capacitor in series with the speaker's input (which is a
transformer, as you know) when driving it with a transistor amplifier might
be a good idea.

By the way, core saturation from an AC current doesn't cause the
inductance's impedance to "disappear" -- it just reduces it.