ARC SP 9 MK III is the best and as all the SP9 uses two tubes , one for the line stage and one for the phono stage. MK III is the only one that uses 6922 the previous models use the 6DJ8/ECC88.
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?