Rocky,
I think we've all missed an important question - have you ever listened to a true high-efficiency system(>97dB)? And have you ever heard the Yamamoto or any other sub-2 watt amplifer?
If not, please be sure to find some system owners in your area and check out their setups before ordering either the Yamamoto or Zu's. Be sure to bring a wide selection of your own favorite listening material.
I like both those components(Zu & Yam), but the jump from regular low efficency to low power/high-eff is a big one that takes some getting used to, careful planning, and lots of fine tuning. I'm not trying to talk you out of your choices, just trying to help you minimize frustration and missed expectations.
High efficiency systems general tend to be far more resolving and ruthless on source material and system components/synergy than higher-power setups with multi-way drivers. At least, that has been my experience over the last 5 years.
The first real shock is that many recordings that you love will seem absolutely unlistenable because of the newly revealed poor recording quality or previous cd/LP abuse. It takes a while to learn to accept or ignore these faults and enjoy the recordings again. This is more common with rock & popular recordings than jazz, classical, etc., yet they still have their own share of bad material.
Good SET amps & high-eff speakers give rpeceding components nowhere to hide. It's like looking at your system with an electron microscope. So, you really have to take car in selecting the preamp and cd/turntable the precede them. Components that seemed dead quiet before will be shwon to actually have annoying loud hum/buzzing. Interconnect choices will have a big differnce on sound.
And then there's your home's power supply. I never knew that I had 60/120Hz hum in my AC line until I made the jump to SET's and high-eff. Now, it drives me crazy.
I had to ground all the outlets in my room. Then, reground my electrical panel to my copper water line. This reduced things significantly, but not enough. I now use a series of isolation transformers and filters.
I'm not saying you a going to have these problems, just don't be surprised if they pop up. High efficency systems are a process instead of a purchase. But, the rewards are stunning when you get close to done. There really is no way to go back once you've crossed over.
And with the Yam+Zu's, you are starting with two fantastic choices.
