Update: ZMFs and Infinity Preamp, and a short comparison to the Oppo PM-1s:
I've been following this thread and been intrigued by all the new options and variations since I bought my ZMF-1s last year. But no comments on those developments. Rather, this is a very short follow up to my previous posts (page 12 #178 and page 22 #319.)
Short because I'm getting ready to go out of town this afternoon.
Got my vintage (~1975) Infinity FET preamp back from the tech today, with its newly repaired headphone circuit. As mentioned previously, this preamp was notable for (among other things) a 6 watt headphone output (load not listed.) I thought it might make a good match for the ZMFs and other planars. Bottom line: it's brilliant! Just a bit leaner in the mids than my Schiitt Lyr, but with greater low-end heft and authority. This preamp was one of the very first to use FETs and the overall sound is very full and liquid - maybe a touch "romantic," with enormous separation of individual musical components and a massive 3-D soundstage (though not as evident with headphones.)
While at it, I pulled out my newly acquired and much-ballyhooed Oppo PM-1s for a comparison to the ZMFs. In short, the two are remarkably similar in sound (perhaps to be expected as they are both planars.) There's a slight variation in male voice presentation, but I haven't listened enough to say more. Nonetheless, the comparo makes me recognize anew the quality of Zach's work. Sonically, a very similar signature at a fraction of the price. Certainly, the PM-1s are sexier and more beautiful, and they are more efficient, and, I think less source-dependent that the ZMFs - but if you want the best bang for the buck, the ZMFs have got to be near the top of anyone's list in their price range (and well above!)
More details when I get back home next week.