check on the maggie owners list, you should be able to find it without too much trouble.
I've had Maggies for years, although I've had to trade down to 1.6qr's in a smaller listening room. Mine are actively bi-amped.
* connecting tube amps directly to the drivers (no cross-over in between) maximizes power transfer, and especially amplifier damping factor. Getting rid of anything in between is a benefit (including the fuse and fuse-holder if you're brave).
* low level crossover between preamp and amp would let you use high quality passive parts that are much less expensive than crossover parts after the amps. The low-level X/O would have to be custom-designed based on the output impedence and input impedence of your respective pre-amp and amplifiers.
* you can customize the amps to the drivers. You can even use solid state for the bass panels, a strong tube amp for the mids, and a delicate little tube amp for the highs. Of course, the input sensitivities of the amps have to match or be adjusted to match.
Lots of good information on this and user experiences over on Audio Asylum: Planar Asylum/MUG=maggies user group.
With bi-ampling each amp is not affected by the others, so you don't get modulation of the treble thru the power supply on heavy musical passages. And, as you surmise, you can get by with a lot less powerful amplifiers overall, since each channel has to manage but a single driver.
I've gone active in my setup because my preamp has high output impedence, which makes it a bad candidate for a low-level crossover. I'm using a MT1 crossover from Linkwitz Labs. You can check out their website for a lot more good information & theory on bi-amping.
Hope this helps!
XTA or Lake technology crossover I'd take 75+75+200 on the amplifiers
Bel Canto or similar 6 channel amplifier will work very very well, reinvent the speaker and in my opinion make it sound excellent.
Right now the 20's are iffy if they can be considered really good in stock form no matter what amplifiers is on it.