Need to learn about Audio Research

I had 3.7’s a few years ago. As has been referenced I heard them at the dealers paired with ARC and they sounded great. That was indeed a classic pairing. I bought them but I couldn’t afford the ARC at the time so I went with classe integrated that sounded good but really didn’t have the power needed. I eventually bought a Pass int-250 which sounded lovely and had the necessary power to play these power hungry speakers. That purchase was started with reading I believe absolute sounds best of show review of the 3.7 with pass amps. I called Reno hi-fi which was the big Pass dealer at the time. He steered me to the Int 250 when I couldn’t quite pay for the recommended pass based on the review ( they were 16-18k ) and the 250 was around 10k.  It was a great choice which served me very well.You should get subs which will take the speakers to another level. You don’t mention a budget but you can find used integrated 250s for 4 to 6 grand. 

You may want to also look at Musical Fidelity. They usually offer amps with larger transformers and capacitors. The other idea is mono amps.

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. 

Class D is attractive, but of the ones I've heard were thin and edgy.

@traudio That can happen if the power supply for the class D is under-built. FWIW there are class D amps now that challenge the best tube amps for smoothness and detail without glare.

I have been a customer of Magnepan and ARC since 1978. I currently on a set of 3.7x Maggies. ( I LOVE THEM!! ) 

I currently drive my Maggies with both a set of Bryston 7BSST Monoblocks and an ARC VT130SE Amp. 

Here is my 45 years of experience with driving Maggies:  

In the 70s ARC and Maggie were "made for each other" because Jim Winey (Mag) and Bill Johnson (ARC) were besties and neighbors. Both men were cutting edge innovators. 

ARC gear is "over engineered" as one person posted- which I take as a compliment. Kind of like Mercedes S class cars are "over engineered".  ARC gear is not for a novice. At least the older models aren't. Tube biasing was challenging on the early ARC units.  Of course MANY audiophiles were technically capable back in the day. Not so now. (Think of millennials with a 4 speed). The newest ARC gear is self-biasing and easier on the tubes. Pretty much zero maintenance. 

As for ARC service I learned that your local guitar amp repairmen (findable through The Guitar Center at the mall) can and do perform service on ARC units. My local guy loves working on them because they are what he calls "Massive American Cool"

As Maggies go your 3.7i are not as current hungry as the early Maggies. IMO You need 200 tube watts.  I love the tube smoothness and holography on the mids/highs. I can't hear a difference between tubes and solid state on the bass. 

You can get a set of ARC Reference 250s used these days between 6-8K of 9-10K for a set of Reference 250SE. (Don't be fooled by the asking prices. Gear sells for 25-35% of retail these days)   If I were your HiFi counselor I'd say the REF 250s would thrill you for decades. 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 absolutely love my 3.7s. When I use my Bryston T-10 8-way line array cone speakers I feel like I'm sporting with a hot new girl while thinking of my favorite girl.

In the end your system should make YOU happy. Work toward that while ignoring the "noise" of other's opinions. Mine included.