Gordon, I've used two models of Maggies for music and home theater, and spent several hours listening to the tri-center with 3.7's at Magnepan.
My first job was in motion picture audio, and spent many hours listening to original elements in the screening room. At the time, I had Tympani 1-D's at home, and when watching movies with VHS hi fi, they blew away anything I heard in the studio, which in turn blew away anything I've ever heard at a theater. Big dynamics can have more bass slam, but the realism of the Maggies more than made up for that. It turns out to be as important for film as it is for music. The realism will astound you.
A big dynamic will have more bass slam than the 3.7's. Not a show stopper, since if you want more bass slam for explosions and such, you can use your subs.
Maggies are more realistic for music than dynamics anywhere near their price point, and, really, most speakers at any price point. The 3.7's will play plenty loud if they have plenty of juice, and louder still if you offload some bass onto the subs. You can still get higher SPL's out of big dynamics, or bigger Maggies. But without knowing what levels you like to listen at, I have no way of knowing if this will matter to you. The 3.7's certainly aren't small speakers -- they play within the range of full-size dynamics.
When it comes to mandolin plucks, snare drums, etc., the Maggies will blow away almost any dynamic speaker. The ribbon tweeter in particular is something special. What the 3.7's won't do is chest-thumping bass. Also, I'd describe the perspective as a window onto a real acoustic space, rather than instruments in your room. They're wall melters -- in a good setup, the walls disappear and it's as if you've been transported into a much bigger space. That's exactly what you need for movies, and for acoustical music. Less so if you want a guitar player in the room with you.
You may well find that you want to liven up your room. Dipoles need/want much less acoustic treatment than boxes.
Tri-Center is unique. It's much more than just three-channel stereo. After you listen to it, when you go back to stereo, stereo doesn't work. It's the weirdest thing. It sounds scarcely better than mono until the next day. I didn't believe it until I tried it myself.
One of the main reasons I've stayed with Maggies all these years is because I do use them in a dual-purpose setup. I find that they give me much of the transparency of stats, and much of the slam of dynamics (the caveat being that the Tympanis have more bass slam and extension than 3.7's -- but then, you're using a sub). In my experience, there's no better speaker for home theater use.
