Why is the Audio Research SP8 so highly regarded?

I have a MRk II SP8 that was modified by Steve Huntley when he was at Great Northern Sound. I don't use the phono section anymore as I have acquired a ARC PH7 so the SP8 is now simply used as a line stage preamp. Am considering replacing with something like a LS26 or Ref 1 { both are in my budget range} Interested from those who might have experience with the SP8 and can offer advice on how much sonically the newer ARC line stage models will improve overall presentation from both analog and digital sources?   
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A little info about the rest of your system helps to get responses that are meaningful. For instance, your SP8 is single ended and the more recent models are balanced. Will you be able to run a balanced system with either of the new preamps?
I have the same question regarding the SP-10 MkII.
I find modern AR gear to be much better sounding. I found the original cold, sterile and perhaps lean.

The modern AR gear looses the lean and cold, but is it better than just neutral?

Listen to Ayre and Luxman for alternative presentations which aren't too euphonic. :)
I had an old AR SP8 back in the day mated to a pair of Cary Audio slm 70 mono blocks driving a pair of custom speaker I built, man what glorious musical sound.

Later I had one of the first AR Ref 1 and it was better in everyday as I recall, transparency, soundstage you name it. Cant comment on the LS 26 but Im partial to the ref series pre. Never heard a cold lean sounding SP 8 or SP 10 pre. to me they where glorious tube sound for their time.

Times change.