Hi Bbchem,
Absolutely love the Tone and I am really enjoy the single driver sound. It took a bit getting used to as the Tone's sound character was a departure from what I'd heard in the past.
While they don't have the pin point imaging of, say, my Focus Audio FS-688 monitors, the quick and natural sound is very addictive. They throw quite a large soundstage as well. Definitely a bit on the warm side, although that is not a bad thing given that the room they're in is a bit "live". The Tones are paired with a REL sub in my work office (see systems link) and two are well suited for each other.
Single driver speakers seem quite popular over here in Asia and Zu, in particular, has quite a following in HK / Singapore / Japan. If you've not heard them or their big brothers, the Druids or Definition Pros, try to. In my opinion, the Definition Pro at around USD 9K is a superb value. Were the FA-888 not the current king of (my) speaker hill, I would seriously consider picking them up and could indeed live happily ever after.
Back to the Tone - my latest purchase of the Kotaro is directly related to my experience with the Tone. While I love my AC V3Ms, With a new office being built in China, this was a good oppurtunity to move them to a bigger space that's better suited to their strengths. Though the Kotaro appears to be two way, it, like the Tone, is a crossoverless wideband single driver with a Murata supertweeter.
The Kotaro has no bass below 70 Hz and, for my tastes, really needs a sub. Aside from that, in many ways it shares much of the Zu appeal with the the upper mid range and highs being the Kotaro's strong suit. It is so clear and effortless (but not etched), that it was frankly startling the first few listening sessions. My hunch is that people whom like single drivers are going to hear a lot more about this speaker.
Never heard horns yet - that's next on my list. Happy listening.
Cheers,
Garry