Audio Research model range

Well I can't help you, but here is a site that should offer you some information.

Good Luck!

ARC Data Base

Audio Research has a web site and a phone...maybe you could call them or a dealer. Value is not one of their hallmarks any longer. I have owned most of the lineup over the years. Budget will dictate what you should be concerned about.

1/2 the pre's used to have phono stages and 1/2 didn't. The SP series had phono, LS did not. Not true with all of their models, especially newer ones. B,C,D and on were updated renditions of the same pre, many times over a 2-10 year period.
With the amps, they have some relation to the power, ie D-70 was a 35 wpc tube amp (very old). Do some googling.
http://www.arcdb.ws/