It's been a while since I owned both the MK 2 and Mk 3. The 3 had gold plated socket pins and I believe both the 2 and 3 had upgraded caps over the previous model. I thought the 2 sounded better with ECC88 Tele's and the 3 with the E88CC. Both were non aggressive on top, soft on the bottom and pleasant and musical rather than strictly accurate. The 3 was much more detailed. Imaging and realism were not their strong points. Of the two the 3 was the one to get.
Audio Research SP9 family
I want to know more about the Audio Research Family. What are the differences among Mk. I, II and III? I learn that the SP-9 family uses only 2 6922- does it mean that the SP9 use tubes in the phono stage and transistors in the line stage (like SP14), or one tube for the phono and one tube for the line? How well was the SP9 accepted when it was new? How does it sound? Is it a good value?