Hi, I can only answer design related questions that are not "how is it implemented".
The direct digital design has its limitation due to the availability of the chip, and also when modulation and demodulation is done in the digital domain, it is harder to optimize for power. When DDA-100 was designed, it achieved a great milestone in combination of sound quality, cost and design elegance. It is a very beautiful product. But NuPrime has since made significant breakthrough in not simply class-D amplifier design, but also switching power supply. This will become apparent in the next few months when you see a flood of new products. Therefore we are now able to come up with something much better and still cost less than $1K.
Ref 20 power supply was the beginning of the renewed R&D effort.
Here's our product positioning:
Ref 20 (this will be the last product that is called NuForce, all future models will be called NuPrime) and other future products that carry the Reference name are the top of the line.
ST-10 and DAC-10H are one level above IDA-16.
And then what's coming in April are a whole line of < $1K products. You will find that the "home/desktop" series are seriously good. Basically we are raising the bar again for what is considered high-end. Today's $800 integrated amp can sound as good as a $5000 integrated ten years ago. We know that from the progress of every generation of products since 2005.
Well, the high-end home theater products should be shipping in May too.
I don't recall IDA-16 using ADC since it has resistor network preamp. It was the DDA that uses ADC.
Jason, would you mind expanding on why you don't feel the direct digital design works for higher power? I loved the DDA-100, and was thinking about an NAD C390DD, but of course these new products of yours are making me question my plans. 
You will really regret it if you don't wait another two months. That's all I can say.
Many high-end brands put Hypex or Icepower in a fancy box, add a linear power supply for differentiation. Some others use off-the-shelf switching power supply. High power, high quality, low noise switching power supply or class-D amp is very difficult to design. That's why there are only a handful of companies in the world doing that. I am quite sure we are the only high-end audio company that actually designs all our amplifier and power supply in-house.
In our opinion, linear PSU is good for lower power design due to cost saving. High-end switching power supply can be made low noise, and it has the speed advantages at high power (obviously it becomes expensive). There is no doubt anymore that our class-D amp can go head to head with any solid state or tube amp, and you can't tell that it is class-D. One of you noticed that IDA-16 is switching at frequency much higher than other amps. That's right. It is extremely difficult to do. 600kHz switching freq gives you such extreme resolution that you are not able to tell that it is class-D amp.
