My sources: Oppo 203 for SACDs (analog in), Chromecast Audio for Youtube Red etc (Optical), Macbook Pro (Optical), Linux box running Daphile (USB).
The USB connection seems to be better than the Optical ones. I think the other digital inputs pass via the other AV DAC. The analog inputs should ideally go through the IDA16 module directly (but might be good to cross check with NuP support)