No, You Cannot Bi-Amp

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.

Bombaywalla, I agree with your take (I think). It's not so much about the theoretical considerations as it is the execution. Maggies have perpetually been subjected (with good reason) to modifications of their crossovers. Peter Gunn made a pretty nice business out of his crossover mods. Others have gone to the trouble to use external active crossovers, and swear that takes the Maggies to a whole new level. If the new crossovers are better than the old stock ones, it is likely due to better parts and better execution, rather than the inherent advantages of the series design. All I know is, the stock 3.7's sound a whole lot better to my ears than the stock 3.6's, which leads me to hope for a similar improvement in the 20.7's over the 20.1's. But the advice remains, go listen, let your ears be your guide.