Need to learn about Audio Research

My experience pretty much mirrors @whart  I well remember hearing the big Maggies with all ARC setups, one of my early references for high end sound, this in 1970's. I only owned a single ARC piece, this SP9MkIII, very disappointing, one of their 'bleached' out offerings.

I too migrated towards horns and SET amps, this gradual move over a number of decades and experience with a variety of amp topologies. I don't doubt you'd find some more recent ARC offerings to match well with the Maggies, my issue is the more powerful the tube amp the greater chance for reliability issues and expensive repairs due to added complexity. High power tube amps put out a lot of heat, heat is the enemy of reliability.

This is no way to buy audio equipment. If you're looking to fail and be unhappy with your system, this is a good way to do it. You have a pair of Magnepan 3.7's. Look at the recommendations you're getting. All are completely different and everyone knows they're right. Its very easy to go out and buy good components. The problem is you can buy all good components but the system can sound like crap because they don't work well together. The 3.7's are not forgiving speakers to work with. You can't rely on other peoples opinions. If you happen to get it right, it will be completely accidental. 

The only way to move forward that makes any sense is to go back to when you auditioned your speakers. What kind of electronics were they using, and what makes you want to buy something different? You need to have some type of reference before you start. And if this was an impulse purchase, you may want to cut your losses now and just get a speaker that's more forgiving to work with. 

@sns Great point about heat being the enemy of reliability. Not only that, but also the fact that the more heat an amp gives off, the quicker the room heats up. In certain climates that is very undesirable.

Living in S.California, I do not want a heat engine in my listening room.

052rc
I didn't audition this pair specifically, but I've heard them in the past and have always wanted a pair. 

A big problem is to visit a "real" dealer is at least 2.5hrs away. It makes it hard to audition or borrow equipment. 

This is why I mostly rely on reviews and forums. 

My history with ARC dates back to 1973, when I got one of the systems @whart referred to above: a pair of Magneplanar Tympani T-I’s bi-amped with Dual 75 and Dual 51 power amps, an SP-3 pre-amp in front (I now own a pair of the Tympani T-IVa’s, a magnificent loudspeaker. But it requires a huge room, which I currently don’t have, so they’re boxed up).

That was obviously a long time ago, and modern ARC electronics are very different from the 70’s stuff. Some people have no problems with their pieces of ARC, others do. If you go with ARC, buy from a local authorized dealer, one with at least some experience with the company’s products. Owning ARC can be like owning an Italian sports car. ARC amps are designed with no fuses in the circuits, so when a tube blows (not uncommon in tube amps), it takes with it a "sacrificial" resistor. That means a trip to the dealer (or ARC), unless you are handy with a soldering gun.

How loud do you listen, and how big is your room? One way to go is to get a tube pre-amp and a solid state power amp. You’ve probably heard Maggies benefit from a high current amp, and the MG3.7i is no exception. A fair number of people have found happiness with the Sanders Magtech amp mated with their Maggies.

If you add a pair of subs to the 3.7's, that will greatly reduce the amount of power you need for the Maggies, and increase their sound quality (if the subs are good enough). Removing the bottom octave (20Hz-40Hz) from the speakers and their power amp cuts the power needs in half!