Need to learn about Audio Research

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.  

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. 

It's hard to argue with you here Smith. There is a little magic in the Ref 6.  To my ear the 5SE sounds better- but I like French Vanilla and you may like Rum Raisin. 

Alternatively, a Ref 5 or 6 are most like a straight wire compared to many- ie: a McIntosh which colors quite a lot. I like their house sound but it does indeed color densely. 

It’s nice to read about folks who owned the gear (from) back in the early days. I guess I’m getting up there- audio history is fascinating to me, and there is so much cool, offbeat equipment that is lost to time. I’m glad ARC is still around.

Special tip of the hat to @kisawyer2 for a great first post!