Most of the advice here is pretty good, except for going to solid state. Tube equipment always sounds better to equivelent solid state, even today. Here is an article that talks about why w/o all the drama. https://spectrum.ieee.org/the-cool-sound-of-tubes This is from IEEE, and it discusses this topic rationally, not with all the arguments and emotions.
Also my wife, who is a fabuluus singer, has perfect pitch, and could care less about equipment except for the final output, has never rated SS above tube all other things held equal. You don't know how wonderful it is to have this type of person living with with regards to stereo setup and equipment selection.
Someday SS may be equivalent or better than tube, but I haven't heard it yet.
Now on observations on durability. Unless you are running your tube equipment using high current setups like Jadis, I've found that tube equipment requires less repairs than solid state. I still have my dad's equipment originally bought in 1961, and most of the tubes are original. Now, I have had all the caps replaced and the switches and dials cleaned and rebuilt, but that was in 2006. Every piece of solid state equipment I have owned has had more issues along the way, and I've had a lot of transistor issues after the equipment gets from 10 years (normal consumer grade) to 30 years (better equipment like what you're looking at). It is a bit of a myth that tube stereo equipment is less durable than solid state. I think that that concept came from the days of tube TV's. CRT's required a lot of current, so tube TV tended to be a pain in the butt and burn out tubes.
I've never actually owned Audio Research, but I have friends who have. It sounds quite good. It is dependable and very well made. The biggest problem I've heard from them is parts availability. Unless that has changed with the current owner, you ended up having to go to them for repairs. They wouldn't sell parts to third parties. I was hoping when McIndosh owned them that that would be corrected. Just don't know the current state. I tend to keep equipment for a long time, and only upgrade when I hear a significant improvement or something breaks and cannot be repaired.
I also get a kick of people citing "recording professionals and musicians" for their blind tests. How were they set up? Who were the recording professionals and musicians? What is their recording pedigree? Do they even care about stereo equipment? What are the parameters? When I was a sceintist, I ran acrass many peer reviewed, double blind studies that were worthless. They had poor controls that were set up to bias the wanted outcome.
Not all recording professionals are good at making recordings. When I was in undergrad, I made better recordings using lesser equipment than the outside professional they hired. He always messed up microphone placement in his intellectual quest to record the "true sound". I saw that many times when I was a more active musician.
I've known a lot of professional musicians: classical, Motown, jazz. I played duets in high school with this guy: https://en.wikipedia.org/wiki/Alan_Baer Many of them, thie first being my contrabass teacher's wife in high school, really have no concept of a good sounding stereo. She used to use a portable record player (mono) with many records stacked on its automatic changer. This piece of equipment ws the worst of the worst. That was her rehearsing studio. Ten feet from her was a much better stereo. A surprising number of pros just don't care about stereo equipment, and would be poor judges of equipment.
At least in classical, I think I understand it. When you are playing in an orchestra, the sound is very diffrent on stage performing than it is when you are in the audience. In the example above, the mono player may have represented better what she heard when performing than what we listeners want, which is the sound from a good performance in a good hall.