Peter, a few words of experience:
Magnepans have three disadvantages IMO...
(1) Space/positioning requirements - small footprint, but require more thought for placement than traditional box speakers (or, at least, are not as immune to misplacement) and require a few feet behind them for optimal sound.
(2) Lack of pinpoint imaging. Their large surface area results in a very wide and realistic soundstage when properly placed, but the line source high frequency and large surface area for mid/low frequency tends to smear the image just a bit. This tends to be coupled to optimal room treatment. I've found that diffusor treatment of side walls enhances the surreal soundstage at the expense of imaging, while absorbent treatment of side walls focuses imaging but takes away the "magic" of magnepans. My methods are pretty crude, but I like the large soundstage better. Otherwise, I'd go with a pair of bookshelf speakers with great imaging accuracy. (note: though this is a shortcoming, they still do quite well for imaging. What I've noticed is that left/right horizontal imaging is not as precise, but you gain a sense of realistic height and depth not often heard with box speakers).
(3) Low end response. The bass is tight, accurate, and very musical, but definitely lacking in output in the lower frequencies... even with the 20.1's. What this translates to is a speakers that (unsupplemented) is perfect for many types of music and not so perfect for many others. HT without a sub is out of the question.
Now, the good things. Integrating a sub is not nearly as difficult as many make it out to be. Maggies sound better with a low Q sub from my experience, and that isn't always easy to find (though I think low Q subs sound better with pretty much any speaker). Crossover and phase settings do take some tinkering, but the result is very satisfying. If you are willing to actively cross over the maggies to remove a bit of the lowest content (say, below 80Hz), then you free up amplifier power and diaphram motion for use in the midbass and mid/high frequencies. The result, when done properly, is a system that can handle any music you wish to play, be it rock, metal, jazz, vocal, piano (ooohh... nothing like classical piano heard through maggies), or orchestral. Actively crossing over (or bi-amping for the larger models) gives you the "slam" many find lacking in maggies.
So far I've been limited to the smaller maggies... MMG's at first, and now SMGc's. I'm heavily leaning towards 3.6's for my new HT. Even the smaller maggies can play loud enough for most rooms given proper amplification.
About amplifiers... maggies like power. More than the recommended power is a good thing IMO. Many have found that the tweeter fuse tends to blow at high listening levels when the amplifier is close to its maximum output. Probably intolerant to the increased distortion. Multiple owners have found that a powerful amp that is running in "cruise control" at high power levels really brings the maggies to life. In my case, I'm using Rotel separates with 170W @ 4ohms into each speaker (I running maggies all around). I'd consider that the bare minimum. Fore 3.6's, I'd recommend around 400W @ 4ohms per channel as a good starting point.
Many like the sound of tubes + maggies, but you definitely give up dynamic range due to the limited power available (unless you have some crazy monoblock tube amps). Good for intimate listening in smaller rooms with many types of music, but not quite the "all around great for
anything" setup I'd want.
Now for my truly biased opinion.
I've extensively auditioned dozens of speakers, including KEF, B&W, Energy, JMLabs, Vandersteen, Dunlavy, Paradigm, and many others. The only speakers I've heard that would make me ever
consider changing from my small maggies and sub are the Dunlavy's.... and at what cost? Instead, I'll probably just upgrade to a pair of true ribbon maggies, build the 'perfect' sub to complement it, and enjoy the goodness.
