As far as how they sound with the HD-800's, I heard them at Jude's, but I'm not an HD-800 expert. Jude said the Zodiac+ sounded "excellent", which he posted earlier. You'll have to await his full review, once we send him a final shipping unit.
The headphone preamp is active, but how it stacks up against stand-alone headphone pre's is a question of taste. The built-in pre-amp is intended to be as transparent as possible. Sometimes some warm distortion, as we all know, is desirable. This should work out to be a proper all-in-one unit that will play nice with more expansive systems, thanks to the XLR outs and de-jittered digital outs.
These have not started to ship yet and the only people who have them are a couple beta testers. I distribute the line in the US, but am not technically employed directly by the company, so I still believe I'm at least partially unbiased. I loved the products and took on the line, not the other way around.
The Zodiac and Zodiac+ should sound the same, depending on how they're used, because the features do differ. The + is more flexible. The regular silver Zodiac also won't ship until much later in the year. The Gold will actually ship next after +.
The reason there are no reviews yet is because we've not sent any out yet for review, but certainly plan on it. We're finishing up one more feature to allow for USB updates of the firmware, as we plan to add more features in future updates to the USB control panel.
As for comparing to a 20K dac, it's important to realize that if you combine the Zodiac+, with 10M and Trinity clocks, this D/A system comes to $12,500, so not exactly mid-fi, imho.
Marcel