I had a mk1 version as I remember. It was a very nice sounding amp but seemed to run out of power very easily. Actually I sold the amp to a buddy who I believe still has it packed away somewhere. I had a pair of monitor type speakers at that time, I don't think they were terribly inefficient. It was 25 years ago and I just don't remember the model anymore.
As I said I replaced the D70 with a Classic 60. The Classic 60 was also rated at 60 watts but never seem to run out of power or sound thin. I later bought a pair of Soundlab Dynastats which I am sure were far less efficient. The Classic 60 still never seemed to run out of power in the same way. Granted the Classic 60 is a Hybrid design and not a pure tube amp.