Hi there,
I've heard a 'D' and own a 'C', which is my daily driver. I've fully rebuilt it and it sounds very, very good to my ears. Its a tricky comparison between the two, given the 'D' was in a different location, and had different peripherals. One thing to consider is, although you auditioned it on similar speakers, the room was obviously different. That in itself has a tremendous impact on the sound you hear. It has been said 'the same speakers sound entirely different in a different room', so of course, following that statement, the amp would also. Different spaces have vastly different nodes, reflections, peaks and nulls, and boundary influences creating an entirely different presentation, which is why I tend to audition in my room when possible. Anyhow, its certainly something to consider before making decision...
Best of luck though, neither would be a disappointment in my view.
John