I have an NTK and don't find it harsh/nasaly/digital. Many have pointed out that the NTK is extremely sensitive to the tube more than one would expect. Mine has an EH tube in it - so maybe start with opening it and seeing what it has. Most of the people who complain about the harshness didn't come stock with the EH tube (or they are used to 47s, which would likely make an NTK sound harsh LOL).
Mine is paired with a GT Brick and sounds very warm. EQ depends on the voice and song. I usually find myself boosting 4.7k, and dipping 220 or 270 ever so slightly.
Also, do you get the harshness WITHOUT the distressor??
Hmm, i also am using NTK into Brick (into scarlett 6i6)
Ive got a NOS mullards in both the NTK and Brick (and a Sylvania for the subminiature). Havent yet done enough recording with it to get a feel for its sound, but did some intense listening to them while rolling valves, and definately not harsh or nasal.