1. Nano > wiim pro+, both digital out and int. DAC; both on 5V/3A LPS or IFi ipower X;
2. Comparing Nano and Ultra is trickier (not on the same footing) because Ultra does not have access to LPS unless you mod it with, say, Teddy Pardo LPS or others. Nevertheless, with this difference:
Nano w/ LPS > Ultra, both digital out and int. DAC.
3. Nano w/ LPS ~ Ultra w/ good DDC (f.g. Gustard U18). Apparently, this got to be digital out. But still, Nano w/ LPS sounds smoother without much hint of digital glare.
(*I have repeated this several times and sort of tired of it. Many others could testify this as well. If you are not convinced, that is fine and continue enjoying music with Wiim. Appreciate the music listening without worrying about the equipment.)

