The Hovland combination is excellent by any measure. As I've written before, despite the high efficiency, Zu speakers, especially Definitions, make good use of moderate to high power. The main issue to consider is that at 125w/ch, you are running a push-pull tube amp. There's a subtle grunge in the push-pull crossover signal handoff that is absent in SET, and which isn't especially noticeable until you experience its absence. An even excellent push-pull tube amp sounds slightly blurred and congested to me, after years of listening to big-glass SET. On the other hand, push-pull tube amps usually have better bass control and sound (and measure as) more strictly linear, all other things being executed to an equal standard. What is surprising to many who hear it for the first time, is how an 845 SET amp rated for 25w can sound equally or sometimes more dynamic than a 100+w push-pull tube amplifier, on a bursty, revealing and efficient speaker like Definitions.
You have to experience at length SET amplification to understand how it fits your perception of convincing musical sound. A Zu speaker is the perfect speaker to explore this with, and there is perfect concept continuity in mating a single-ended tube amp with a crossoverless loudspeaker. Just don't do it with an old-school slow and sweet kind of SET. At the expense level you're already playing, you can afford a good, objective SET choice. There's no reason you can't mate your excellent Hovland preamp to a good SET amplifier, so no need to take depreciation loss on two pieces if you decide to try the SET power amp route.
The Berning OTL option is also highly credible musically and convincing. Going transformerless but retaining the push-pull topology gives you some of the immediacy of SET but not quite the same thing. Berning has a truly clever OTL circuit that uses an RF carrier signal through a high frequency transofrmer to handle impedance matching without the audio-compromizing effects of an audio frequency transformer. The Berning gear, including the ZOTL preamp, have a specific brand sonic character, which is fast, dynamic and highly transparent. Some people hear it as accurate, others as a little sterile and lacking full tonal body. It's undeniably good. But so is your preamp mated to a suitable SET amp, which if selected well will give you a more holistic, toneful presentation with lots of body. It costs more to get the speed and sheer openness of the Berning in an SET design that delivers the full holistic sound that topology is capable of. Choices.
I think in many respects, the Berning sound can also be closely acquired in solid state in the form of Lavardin.
Phil
