porco_rosso
Hi I have tried the first few bars of this piece and others with ff that I have played even harder on my NU1X and I still don't notice the smoothing problem discussed in this thread. In my case I have always adapted the pianoteq velocity curve to fff values around 115. With the internal Yamaha CFX sound I have tried lowering the keyboard sensitivity to the softest one to get a higher volume with the same loudness. In both cases, IMO, the sound I get fff is sufficient for my expectations and my technique.
Knowing a type of works or repertoire was to explore in which margins the error appears in the interpretation. For example when going from mf to fff, or from ff to fff, several fff chords in a row in a specific measure, etc. You also don't make the same strength playing a fff chord as playing a single fff note, etc. In any case to know something related to musical practice and not to isolated tests of key playing with great force or hand positions that may differ from the interpretation. In no case I have referred to the fact that one has to play the piano as I do, since each one of us has our own technique and sensibility.
As a conclusion on this debate on my part, I think it has been good to see if the instrument has a generalized problem or not. Some of us have not been aware of the problem or others have. In your case it has been your experience and you have already proceeded to return it. Whatever happens, I wish you the best in your future purchase and that the model you purchase meets all your expectations.