Is Audio Research SP-6 considered a good model?

Very good piece in its day and still should be very good.However I would invest in a test bench professional to go thru it and get as much out of it as possible..I think there is a company called "Great Northern" that specializes in upgrades etc on Audio Research vintage stuff.. For what you will invest you won't find anything,thats for sure...
Theres also a company in Framingham,Mass called Natural Sound that has been selling/service for many years.They did a nice job on a SP8 of mine awhile back.They are still around at the same location.....Good Luck

There were so many versions of the SP-6, and not all of them were considered good, that it is really difficult to answer your question. If it is the original 6, it could definitely be improved with cap and resistor upgrades for probably not too much money but you have a competent technician do this work. ARC will charge you an-arm-and-a-leg to do this and I really can't say if this would represent good value (but I doubt it).

ARC estimated $700-800 for the work. I know there were other models with letters e.g. SP-6A... don't know if there were different versions of the SP-6. I'm also wondering what power amp would pair well with the SP-6......