I've owned the Onyx and the Ambre for about three years now and have had no issues and the sound is as described above. The I2s connection sounds best to me. Very Organic and detailed at the same time. I recently upgraded the four modules in the Onyx to their latest DAC 3 modules which doubled the number of DAC chips to a total of 16 now.
Cees mentioned that now my Onyx is on par with the Sonnet Morpheus and to my ears it was a very nice improvement. More open and a little more detailed sounding. The Onyx without these DAC upgrades was a bit warmer and laid back which is good as well but I do prefer the extra detail and openness. I read a review a year or so ago regarding the Morpheus and the reviewer stated that it sounded like a cross between a traditional NOS sound and the more common sabre type DAC sound which to me is exactly what I want and a compliment to the Morpheus.