This is the first I have ever heard of anyone claiming better build quality on one over the other; having owned the II, I don't know what JRDG could of done to improve upon the build quality, it was second to none. I am sure JRDG would refute this claim.
I will throw in my hat as one who enjoyed the CN-II a lot, I know this doesn't address your question.
Here is a reply from Rich Maez from JRDG in answer to a question I had for him in the past.
"The CN I and CN II differ completely by power supply. The CN II has a much more powerful (50% more power) supply and therefore has much better control and power into low frequencies. It also has a separate front end supply that allows the unit to dedicate more power to large transients and make the CN II much more dynamic. High frequency distortion was reduced quite a bit with the second generation unit as well, so it has a much more open and extended high frequency response."
I will throw in my hat as one who enjoyed the CN-II a lot, I know this doesn't address your question.
Here is a reply from Rich Maez from JRDG in answer to a question I had for him in the past.
"The CN I and CN II differ completely by power supply. The CN II has a much more powerful (50% more power) supply and therefore has much better control and power into low frequencies. It also has a separate front end supply that allows the unit to dedicate more power to large transients and make the CN II much more dynamic. High frequency distortion was reduced quite a bit with the second generation unit as well, so it has a much more open and extended high frequency response."