As a happy Zen Select owner, I'll just say here, re: the "EX-Mod" trafos, which are not designed for low impedence loads, that some of us have encountered significant hum with them. Steve Deckert says they can be very quiet, however. They add more "weight" to the presentation, but you'll need more power, IMHO. A pity,'cause they really are outstanding amps with efficient speakers.
Don