best amp for Magnepan 3,7

Unfortunately, the 3.7 can't be bi-amped, otherwise I suggest Threshold S500 for LP 700Hz with Bryston 10B.
I also suggest CAT SL1 Sig. MK2 for pre-amp.
I am using these audio gears for my Magie system consisting of Tympani IV bass panel and MGIII.
My room is 6x8 m with 2.8 m ceiling height, the sound is fantastic.

I just purchased a brand new Conrad Johnson Premier 350 SS amp to drive my Maggies. Eager to how it compares to my VAC 300.1a.

CJ 350 is the cat's meow. Sweet treble plus absolute punch.

I am using an Audio Research D400II to drive my 3.7s. It has tons of current with 400 watts to the 4 ohm load and is very neutral IMO. Tried two of them bridged for mono since I was bi-amping an earlier model, but that makes them a 2 ohm load and while they could drive them, prefer the single amp in 2 channel mode. You get find them used for under around 1600-1900

Just for kicks now using the other AR amp to drive a pair of Klipsch Cornwalls. With 100db effeciency now I can annoy neighbors for blocks if I so choose :-)

A little apples to oranges, but I happily run my MMGs with a 40 Watt tube amp at very satisfying levels. Of course, it helps that I use a simple crossover to filter out 65hz and below, but that mainly helps clarity. I don't think it makes much difference as far as absolute spl is concerned.