I have not heard an amp with the really high end output transformers. THere is consensus among everyone I talk to that the high end output trannies are key, much more so than caps or "silver wire".
I built a cheap little push-pull amp from a kit, and the sound is really quite good (ok i did use cheap silver solder). . I am VERY satisfied with the ZEn. I would recommend you at least hear it, since it has a 30 day guarantee.
I plan on building a 300 B amp...BTW, i would also suggest you look at
www.angela.com the DIY section...there is a nice 300b amp there as well.