Charles1dad, What you say is true but about a different post- so in that we regard we are writing about two differnt things, but perhaps I take things much more literally than you.
What should be pointed out here is that a speaker that is 6 ohms is not going to match a transformer-coupled amp *ideally* either, unless that amplifier has a 6 ohm tap.
In the case of a small OTL, you only have to use a set of ZEROs. In the case of the ZERO, if you look that the website-
http://www.zeroimpedance.com-you will see that the autoformer is treated more as a set of ratios than a specific impedance like 4 or 8 ohms. What this means is that if you have something like an S-30, and using the 2:1 ratio, that the amplifier will be driving a 36 ohm load. As far as the S-30 is concerned, this is ideal. The speaker does not need a *lot* of power, and the 45 watts that the S-30 will make in this example will really wake the speaker right up, better than most transformer-coupled amps.
Now you may not realize this but we used to make a product like the ZERO about 20 years ago, we stopped when the ZERO came out because it was a lot easier to explain the ZERO than it was our own product!
People were always asking 'Don't you obviate the OTL thing when you do that?' and the answer is no. Its funny how people had this story that an OTL had to be a certain way, and were equating the ZERO and its predecessor with regular output transformers, and there is a huge gulf between the two. The bottom line though is that it is just a way to make music, and I've never seen it as anything else.
That is why I always recommend to our dealers that they have a set of ZEROs on hand.