Need to learn about Audio Research

If you do a search you can find Mike Fremer's video tour of the ARC factory. With the recent acquisition by Acora little if anything has changed. Dave Gordon can be seen in Fremer's video doing listening-tests of each and every Ref Series amp that leaves the building and he is using.....Magnepans just as ARC has utilized for sound testing for many decades. l

I am a long time ARC owner and fan. I believe that the preamp is the heart and soul of a top tier audio system and few will argue that ARC has built a reputation for building some of the best preamps out there. I fully accept the argument that ARC amps can be a pain and arguably don't sound special but please keep in mind that if you want to guaranty optimum synergy between preamp and amp, you have to think hard about pairing an ARC preamp with an ARC amp. And....the latest series of Ref amps feature self-biasing (finally) and soft-start circuitry (finally!!!) which makes then more reliable than ever. 

Also consider that not all tube preamps and amps are fully balanced from input to output and ARC preamps and amps are in the Ref Series and also keep in mind that all ARC gear continues to be built entirely by hand in the MN factory. 

My biggest criticism of ARC is that they went all-in with the KT150 tube which has not proven to be a reliable tube due to terrible QC at the New Sensor factory. I also join with the others above that ARC charges outrageous amount for matched sets of replacement tubes and for service.  Perhaps that is why they are once again coming out with SS amps. 

I'd use a used Ref 5 or 6 preamp as they are arguably "straight wire with gain" and don't color tamper with the input signal.

I don't quite agree with this, fwiw. The Ref 6 when running balanced does something to the input to make it more spatially dense and atmospheric. You can go round and round as to whether it simply preserves something in the recording lost by other preamps or adds something-I believe it is the latter. 

Then again, I always thought the "straight wire with gain" is one of the most meaningless cliche's among the thousands in audio. Two preamps can be "straight wires with gain" and yet sound completely different, particularly if one if solid state and one is tubed.