CLASSE Model 6 and DR-6 differences

Likewise, I cannot completely answer your question, but can offer some insight. I also purchased a Classe DR-4 and had it upgraded to the newer Model Four. Thus, the Model 6 is newer. Sonically, the DR-4 was warmer and smoother. The Four was airier, had a slightly larger soundstage and I guess could be called more "neutral", whatever that means. It was not as warm sounding as the DR-4, but was more revealing. These are not big differences but they are noticeable.

I can't completely answer your question, but I do have a tid bit of info on the subject. The DR stands for David Reich, who was one of, or the designer of the preamp. I believe that after he left the company, they dropped the DR from the model name. I had a DR 4 and Reich's signature was printed on the circuit board. Incidentally, I tried out a DR 6 and actually preferred the DR 4 in my system. The 4 sold new for $1600. The phono section, however in the 6 was a bit superior.