Well,CDC, it sounds to me like a classic case of a particular design doing some things very well, and some things not so well. Many of the things you didn't like about the Brentworths are not weaknesses in the other brands of single-driver systems. For example, punchy dyanamics and excellent high-end extension are strong suits of the Lowther single-drivers. They are usually somewhat bass-limited by the back-horn designs, but will generally do about 40Hz. As low-excursion 8" drivers, they are never going to "rock your world" in the bottom end category. But, it is there, and solid, and accurate. Fostex will roll off a little early in the high-end, and so will Diatone.
One of the things that concerns me about their claims of 20Hz bottom end, is that your listening experience does not seem to bear out their claims. So, at best, in my book, these claims are doubly questionable now.
About the proper soundstaging you heard, that is a characteristic of good single-driver systems. The point-source and phase coherence really enhances imaging and soundstaging.
I'm not really sure what you mean by "distorted immediacy" and "pleasant distorted" sound about SET's. I don't seem to get that impression at all. I understand they have some issues at some frequencies, but I can hardly believe that the high end Wyetechs were having transformer-related problems. Perhaps it was the speaker's shortcomings you were hearing. Also, I find the taste for bass "punch" is highly variable, with no 2 people really agreeing with how much there should be, for enjoyable listening.
I'm glad you were able to inform me about your listening experience with the Brentworths, since I had no contact with them, and have benfitted from yours. Thanks.