I have been using single drivers with SET amp for awhile now, and I really like it.
The "Lowther Honk(or shout)" is much less with the new series of drivers that has been out for about a year or so, now. Also, it is much better after a long time of break in(500 hours) which most dealers don't have time to put on their demo speakers. Additionally, I have developed a cone treatment that virtually eliminated any residual aspects of the "shout"(not for sale). The Abbey is actually an iteration of a Voigt Pipe enclosure, and is similar to what I use with my Lowther EX3 drivers. Very enjoyable for what it is designed to do.
I would say that a true SET amp is a requirement on these kinds of speakers, since they have a synergy with single driver speakers that is not matched by push pull type amps. Lower power is better, with a 3 watt 2A3 SET or a 2 watt 45 SET being about perfect for these Lowther driver systems. A 300B would probably be better for the Fostex drivers or the Jordans. I use a 2 watt 45 SET ZOTL by David Berning with 12v battery power and choke loading, and it sounds extremely good on my modified Lowther Voigt Pipe system. No problem achieving 105db peaks at 1 meter with this setup.
As far as these systems being too revealing for poor program material, this is quite true. Poor program material, especially in CD, is sometimes unlistenable. As a result I use LP playback only on my system, which gives me a much more palatable overall result. But there are some LP recordings that are very poor also. When you have a very revealing system, it will reveal a poor recording just as fast as a poor product or matchup in the system synergy. You really have to know what you are doing to get a system like this sounding just right, because even slight errors in synergy or product selection will become painfully obvious when listening. There is simply no place for any flaw to hide. But when you get it right, it will deliver musical performance like very few, if any, other kinds of systems can.
In a properly sized room for a system like this, it is possible to get very close to live volume levels for the kinds of acoustic or club music that are typically played on systems like this. No, it is not going to simulate the live SPL of Led Zeppelin at Shea Stadium, but it will do rock and roll very nicely for the SPL that most people would be satisfied with in their living rooms, and not do much hearing damage in the process. If you are a headbanger, then this is not the system for you. If you want a very musical system that has micro and macro dynamics to die for, which is what I think is the heart of the emotional content of the music, then this is a great system for you.
I applaud you for reporting your findings on this type of system to the members, because I think there is still some lingering doubt that a low power, single-driver system can be a satisfying audiophile package. In my opinion, it is about the only type of system that I could live with anymore, because it does what none of my other more "conventional" high power SS or tube systems could do. It delivers music better than any of the more "normal" systems that I have ever heard. Yes, there are flaws which are primarily in deep bass response and some colorations. Nothing is perfect. But these are very good systems that can do some things better than anything else, and should be taken seriously by anybody seeking truly musical reproduction with incredibly live sounding dynamic detail at reasonable SPL.