No, You Cannot Bi-Amp

Sonic benefits:

Transparency
Dynamic Headroom is not jeopardised by either descrepancies of amplifiers or decreased input amplification impedance
Tonal balance

Negatives:

1. 2 cheaper lower powered amps can have more power than one nicer more pricey amp so there are limitation on available options that should IMHO be present in complexed speakers
2. If two amps are absolutely identical, the benefits could be identical to a single amp only with increased power.
3. Y-connector on preamp output may be necessary that decreases an input impedance of amplification again limiting the dynamic headroom.

Ahendler's comment is right on target. The series crossover is not amenable to biamping. My opinion of the crossover in the 3.7's is that is a pretty significant improvement over the stock crossover in the 3.6. I drive mine with Cary 500 MB's, which delivers sufficient current to drive the speakers without biamping. I have heard neither the 20.1's or the 20.7's so I can't comment on those two. Let your ears be the judge.

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I wouldn't know a crossover from a crossbow. I want to get myself a pair of the 20.7 and I'm glad to know that the new design allows you to power the speaker with one amp without having to worry about whether it would sound better with two amps. I'll just make sure the my amps have plenty of muscle at 4 ohms in order to dominate the speaker.
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01-18-12: Elizabeth
In my mind biamping is a 'teenage' phenomenon.
If one is good, two MUST be better.
Yeah a few folks are able, with effort to make it work for themselves.
In general it is a waste of time, if as much effort was made to have one amp work well.
The worst side of it is all the folks who know nothing about it wanting to do it as if it is some easy magic panacea.. Gee I could biamp,,Cool!.... NOT.

OMG, there you are again spewing BS on a topic that you have no technical knowledge of (& once again you have to be reminded of the same). Like in many other similar posts of yours,I have earnestly requested you to not write garbage on a topic esp. if it calls for a technical explanation. This only continues to spread "old wives tales" on the subject matter which disallows this audio community from getting more informed. This request is being made once again....

Mitch4t,
here is a nice (& lengthy) article on Series vs. Parallel Crossovers.
http://sound.westhost.com/parallel-series.htm
You can see (immediately) that the series crossover has only 1 input hence bi-amping is not possible (the author states this himself as well). From this article & the technical measurements it's quite clear to see that (iffffff) the series & parallel x-overs are done right, they are nearly identical (& the author even states this in the concl para) in their performance so this hyperbole of the Maggie 20.7 x-over being much better than its prev revisions due to it being a series x-over is pure BS! The 20.7 xover might/must be better (I've not heard the 20.7 myself) maybe because Magnepan decided to spend the time & patience to do it right after all these years?? (speculation on my part but who knows the exact reason for it being better - certainly not due to it being a series xover...)

Biamping made sense when amplifiers exhibited lots of IM distortion and a high powered amp was 60 watts. Not the case today.

True biamping means that you use a line level crossover. Such a crossover is usually superior to a passive crossover, and much less costly if the passive uses high quality parts. IMHO, the crossover is the chief advantage.

Subwoofers are almost always biamped.