I did evaluate Paul's autoformers and they do work very well.
However the catch is that by the time you pay for the Ultravalve and a set of autoformers to allow useful performance into a 2 ohm load, you have now paid a lot more than a 200 watt per channel Ultra 350 or 300 watt per channel Ultra 550 amplifier would cost, and both of these will have no problems with low impedance loads, and provide musical performance the equal of the Ultravalve.
Thus I don't think the autoformer route is the most cost effective way to better music with inefficient speakers.
Regards,
Frank Van Alstine