Comparing the specs, the only thing that is different than the Nu Audio 1.0 is the op-amp and some capacitors. I doubt that's going to be a noticeable difference to existing Nu Audio owners like myself.
To my ear, there was an immediately noticeable difference. I like this difference, myself, but this is sort of the experimental side of audio. I imagine that some people will like the more analytical signature of the original NU Audio compared to the NU Audio Pro, whereas others will prefer the somewhat warmer, airier and more dynamic NU Audio Pro. It reminded me often of how I've described the difference between a pair of Focal Elear and Audeze LCD-2 CB headphones. Both great, but very different signatures. Again, that's my impression of it, so feel free to take it with a grain of salt.