The DAC19 was delivered quickly after I put in the order, and I immediately let it burn in for over a week. I gave it a brief listen on the first day, and it's not spectacular. After over 100 hours, it started to settle and got much better. You'll need to allow a lot of break in time.
Feeding the DAC19 via USB: the implementation was not bad, and it was straightforward via OSX. The only thing that one should be aware of is that there is a limit of 192kHz when played with Audirvana. Initially, I was wondering why there was no sound coming out of the USB, but adjusting the limit on app to only go up to 192 made the problem go away.
Via the optical: no problems.
Coaxial: haven't tried it yet.
Build: it's solid aluminum for the case. It's heavy. It's bigger than I thought. The RCAs stick out a bit at the back. The input selector knob is solid. It's straight forward: 3 different input selections, 1 button on/off, 1 button for inversion. It's all business, no bling except for the blue LED 'on' light.
Good: new R2R DAC at a competitive price. I runs "warm"--good heat dissipation. Sound. ACSS is suppose to help with your hifi chain. Kingwa sometimes answers your email if you have questions about his products.
Not so good: it's huge, even though this is a "small" DAC. ACSS unless you have an Audio-gd amp.
Sound: Sorry, I'm not flowery with descriptions. Smooth. Warm. Realistic. Wow. Previously, I had a tube buffer to "smooth out" some of the sound in my old mid-fi stereo system, but the DAC19 was able to present a smooth, realistic sound without the buffer. I now understand the fuss with R2R, and going forward I'd probably would want to upgrade along the same (i.e., R2R) for more detail, better imaging. I've heard some very expensive D-S DACs, and most don't have that presentation that the DAC19 has with some of the music I enjoy playing (e.g., vocals, acoustics). It may not have the same detail, imaging, etc but the sound is more involving and...real.
Value: it punches above its weight. It could be worth several hundred dollars more. I didn't put it to use as my headphone listening system (yet), but mainly for my stereo system (tv, music streaming) with speakers. I could easily have it as part of my headphone listening chain. And for that...
I would have wanted to: skip this for the Master 7, Reference 10.32 or an Ygg. Along with a very good amp, and run everything through balance mode. But for that I'd have to lay out some serious cash for both an R2R DAC and an amp that will be able to handle that uber level. The reality is that skipping the DAC19 in favor of the next level would delay having an R2R DAC for a much longer while. Also, the just mentioned super DACs are really huge--a real factor for my modest living environment.
Wish: slightly smaller size; ability to put the DAC on its side (actually I can do that now, but I'd have to take off the feet and put silicon nubs, etc on); that the RCAs didn't protrude out so much because it's not a small box as it is; also want it to be balance output so I can use it with my balance headphone amp (but it's not going to happen at this price point).
As a DAC for my old stereo system, it's great as it's only RCAs to my speaker amp. You get USB, coaxial, optical without having to fuss that much with an older R2R DAC (if you can find one at a decent price).
The DAC19 for now is a keeper for my stereo system. Although, I'm really considering the path to a higher spec R2R.
Time to save up.
